# Copyright 2015 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""This API defines FeatureColumn abstraction.

FeatureColumns provide a high level abstraction for ingesting and representing
features in tf.learn Estimator models.

FeatureColumns are the primary way of encoding features for pre-canned
tf.learn Estimators.

When using FeatureColumns with tf.learn models, the type of feature column you
should choose depends on (1) the feature type and (2) the model type.

(1) Feature type:

 * Continuous features can be represented by `real_valued_column`.
 * Categorical features can be represented by any `sparse_column_with_*`
 column (`sparse_column_with_keys`, `sparse_column_with_vocabulary_file`,
 `sparse_column_with_hash_bucket`, `sparse_column_with_integerized_feature`).

(2) Model type:

 * Deep neural network models (`DNNClassifier`, `DNNRegressor`).

   Continuous features can be directly fed into deep neural network models.

     age_column = real_valued_column("age")

   To feed sparse features into DNN models, wrap the column with
   `embedding_column` or `one_hot_column`. `one_hot_column` is recommended for
   features with only a few possible values. For features with many possible
   values, `embedding_column` is recommended.

     embedded_dept_column = embedding_column(
       sparse_column_with_keys("department", ["math", "philosphy", ...]),
       dimension=10)

* Wide (aka linear) models (`LinearClassifier`, `LinearRegressor`).

   Sparse features can be fed directly into linear models.

     dept_column = sparse_column_with_keys("department",
       ["math", "philosophy", "english"])

   It is recommended that continuous features be bucketized before being
   fed into linear models.

     bucketized_age_column = bucketized_column(
      source_column=age_column,
      boundaries=[18, 25, 30, 35, 40, 45, 50, 55, 60, 65])

   Sparse features can be crossed (also known as conjuncted or combined) in
   order to form non-linearities, and then fed into linear models.

    cross_dept_age_column = crossed_column(
      columns=[department_column, bucketized_age_column],
      hash_bucket_size=1000)

Example of building tf.learn model using FeatureColumns:

  # Define features and transformations
  deep_feature_columns = [age_column, embedded_dept_column]
  wide_feature_columns = [dept_column, bucketized_age_column,
      cross_dept_age_column]

  # Build deep model
  estimator = DNNClassifier(
      feature_columns=deep_feature_columns,
      hidden_units=[500, 250, 50])
  estimator.train(...)

  # Or build a wide model
  estimator = LinearClassifier(
      feature_columns=wide_feature_columns)
  estimator.train(...)

  # Or build a wide and deep model!
  estimator = DNNLinearCombinedClassifier(
      linear_feature_columns=wide_feature_columns,
      dnn_feature_columns=deep_feature_columns,
      dnn_hidden_units=[500, 250, 50])
  estimator.train(...)


FeatureColumns can also be transformed into a generic input layer for
custom models using `input_from_feature_columns` within
`feature_column_ops.py`.

Example of building non-tf.learn model using FeatureColumns:

  # Building model via layers

  deep_feature_columns = [age_column, embedded_dept_column]
  columns_to_tensor = parse_feature_columns_from_examples(
      serialized=my_data,
      feature_columns=deep_feature_columns)
  first_layer = input_from_feature_columns(
      columns_to_tensors=columns_to_tensor,
      feature_columns=deep_feature_columns)
  second_layer = fully_connected(first_layer, ...)

See feature_column_ops_test for more examples.
"""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import abc
import collections
import math

import six

from tensorflow.contrib import lookup
from tensorflow.contrib.layers.python.layers import layers
from tensorflow.contrib.layers.python.ops import bucketization_op
from tensorflow.contrib.layers.python.ops import sparse_feature_cross_op
from tensorflow.contrib.layers.python.ops import sparse_ops as contrib_sparse_ops
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import sparse_tensor as sparse_tensor_py
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import init_ops
from tensorflow.python.ops import math_ops
from tensorflow.python.ops import parsing_ops
from tensorflow.python.ops import sparse_ops
from tensorflow.python.ops import string_ops
from tensorflow.python.platform import tf_logging as logging
from tensorflow.python.util import deprecation


class _LinearEmbeddingLookupArguments(
    collections.namedtuple("_LinearEmbeddingLookupArguments",
                           ["input_tensor",
                            "weight_tensor",
                            "vocab_size",
                            "initializer",
                            "combiner"])):
  """Represents the information needed from a column for embedding lookup.

  Used to to compute DNN inputs and weighted sum.
  """
  pass


class _DeepEmbeddingLookupArguments(
    collections.namedtuple("_DeepEmbeddingLookupArguments",
                           ["input_tensor",
                            "weight_tensor",
                            "vocab_size",
                            "initializer",
                            "combiner",
                            "dimension",
                            "shared_embedding_name",
                            "hash_key",
                            "max_norm",
                            "trainable"])):
  """Represents the information needed from a column for embedding lookup.

  Used to to compute DNN inputs and weighted sum.
  """
  pass


class _FeatureColumn(object):
  """Represents a feature column abstraction.

  To distinguish the concept of a feature family and a specific binary feature
  within a family, we refer to a feature family like "country" as a feature
  column. For example "country:US" is a feature which is in "country" feature
  column and has a feature value ("US").
  This class is an abstract class. User should not create one instance of this.
  Following classes (_SparseColumn, _RealValuedColumn, ...) are concrete
  instances.
  """
  __metaclass__ = abc.ABCMeta

  @abc.abstractproperty
  @deprecation.deprecated(
      "2016-09-25",
      "Should be private.")
  def name(self):
    """Returns the name of column or transformed column."""
    pass

  @abc.abstractproperty
  @deprecation.deprecated(
      "2016-09-25",
      "Should be private.")
  def config(self):
    """Returns configuration of the base feature for `tf.parse_example`."""
    pass

  @abc.abstractproperty
  @deprecation.deprecated(
      "2016-09-25",
      "Should be private.")
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    pass

  @abc.abstractmethod
  @deprecation.deprecated(
      "2016-09-25",
      "Should be private.")
  def insert_transformed_feature(self, columns_to_tensors):
    """Apply transformation and inserts it into columns_to_tensors.

    Args:
      columns_to_tensors: A mapping from feature columns to tensors. 'string'
        key means a base feature (not-transformed). It can have _FeatureColumn
        as a key too. That means that _FeatureColumn is already transformed.
    """
    raise NotImplementedError("Transform is not implemented for {}.".format(
        self))

  # pylint: disable=unused-argument
  def _to_dnn_input_layer(self,
                          input_tensor,
                          weight_collection=None,
                          trainable=True,
                          output_rank=2):
    """Returns a Tensor as an input to the first layer of neural network."""
    raise ValueError("Calling an abstract method.")

  def _deep_embedding_lookup_arguments(self, input_tensor):
    """Returns arguments to embedding lookup to build an input layer."""
    raise NotImplementedError(
        "No deep embedding lookup arguments for column {}.".format(self))

  # It is expected that classes implement either wide_embedding_lookup_arguments
  # or to_dense_tensor to be used in linear models.
  # pylint: disable=unused-argument
  def _wide_embedding_lookup_arguments(self, input_tensor):
    """Returns arguments to look up embeddings for this column."""
    raise NotImplementedError(
        "No wide embedding lookup arguments for column {}.".format(self))

  # pylint: disable=unused-argument
  def _to_dense_tensor(self, input_tensor):
    """Returns a dense tensor representing this column's values."""
    raise NotImplementedError(
        "No dense tensor representation for column {}.".format(self))

  def _checkpoint_path(self):
    """Returns None, or a (path,tensor_name) to load a checkpoint from."""
    return None

  def _key_without_properties(self, properties):
    """Helper method for self.key() that omits particular properties."""
    fields_values = []
    # pylint: disable=protected-access
    for i, k in enumerate(self._fields):
      if k in properties:
        # Excludes a property from the key.
        # For instance, exclude `initializer` from the key of EmbeddingColumn
        # since we don't support users specifying different initializers for
        # the same embedding column. Ditto for `normalizer` and
        # RealValuedColumn.
        # Special treatment is needed since the default str form of a
        # function contains its address, which could introduce non-determinism
        # in sorting.
        continue
      fields_values.append("{}={}".format(k, self[i]))
    # pylint: enable=protected-access

    # This is effectively the same format as str(self), except with our special
    # treatment.
    return "{}({})".format(type(self).__name__, ", ".join(fields_values))


# TODO(b/30410315): Support warm starting in all feature columns.
class _SparseColumn(_FeatureColumn,
                    collections.namedtuple("_SparseColumn",
                                           ["column_name", "is_integerized",
                                            "bucket_size", "lookup_config",
                                            "combiner", "dtype"])):
  """Represents a sparse feature column also known as categorical features.

  Instances of this class are immutable. A sparse column means features are
  sparse and dictionary returned by InputBuilder contains a
  ("column_name", SparseTensor) pair.
  One and only one of bucket_size or lookup_config should be set. If
  is_integerized is True then bucket_size should be set.

  Attributes:
    column_name: A string defining sparse column name.
    is_integerized: A bool if True means type of feature is an integer.
      Integerized means we can use the feature itself as id.
    bucket_size: An int that is > 0. The number of buckets.
    lookup_config: A _SparseIdLookupConfig defining feature-to-id lookup
      configuration
    combiner: A string specifying how to reduce if the sparse column is
      multivalent. Currently "mean", "sqrtn" and "sum" are supported, with "sum"
      the default. "sqrtn" often achieves good accuracy, in particular with
      bag-of-words columns.
        * "sum": do not normalize features in the column
        * "mean": do l1 normalization on features in the column
        * "sqrtn": do l2 normalization on features in the column
      For more information: `tf.embedding_lookup_sparse`.
    dtype: Type of features, such as `tf.string` or `tf.int64`.

  Raises:
    TypeError: if lookup_config is not a _SparseIdLookupConfig.
    ValueError: if above expectations about input fails.
  """

  def __new__(cls,
              column_name,
              is_integerized=False,
              bucket_size=None,
              lookup_config=None,
              combiner="sum",
              dtype=dtypes.string):
    if is_integerized and bucket_size is None:
      raise ValueError("bucket_size must be set if is_integerized is True. "
                       "column_name: {}".format(column_name))

    if is_integerized and not dtype.is_integer:
      raise ValueError("dtype must be an integer if is_integerized is True. "
                       "dtype: {}, column_name: {}.".format(dtype, column_name))
    if dtype != dtypes.string and not dtype.is_integer:
      raise ValueError("dtype must be string or integer. "
                       "dtype: {}, column_name: {}".format(dtype, column_name))

    if bucket_size is None and lookup_config is None:
      raise ValueError("one of bucket_size or lookup_config must be set. "
                       "column_name: {}".format(column_name))

    if bucket_size is not None and lookup_config:
      raise ValueError("one and only one of bucket_size or lookup_config "
                       "must be set. column_name: {}".format(column_name))

    if bucket_size is not None and bucket_size < 1:
      raise ValueError("bucket_size must be at least 1. "
                       "bucket_size: {}, column_name: {}".format(bucket_size,
                                                                 column_name))

    if ((lookup_config) and
        (not isinstance(lookup_config, _SparseIdLookupConfig))):
      raise TypeError(
          "lookup_config must be an instance of _SparseIdLookupConfig. "
          "Given one is in type {} for column_name {}".format(
              type(lookup_config), column_name))

    if (lookup_config and lookup_config.vocabulary_file and
        lookup_config.vocab_size is None):
      raise ValueError("vocab_size must be defined. "
                       "column_name: {}".format(column_name))

    return super(_SparseColumn, cls).__new__(
        cls,
        column_name,
        is_integerized=is_integerized,
        bucket_size=bucket_size,
        lookup_config=lookup_config,
        combiner=combiner,
        dtype=dtype)

  @property
  def name(self):
    return self.column_name

  @property
  def length(self):
    """Returns vocabulary or hash_bucket size."""
    if self.bucket_size is not None:
      return self.bucket_size
    return self.lookup_config.vocab_size + self.lookup_config.num_oov_buckets

  @property
  def config(self):
    return {self.column_name: parsing_ops.VarLenFeature(self.dtype)}

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return "{}".format(self)

  def id_tensor(self, input_tensor):
    """Returns the id tensor from the given transformed input_tensor."""
    return input_tensor

  # pylint: disable=unused-argument
  def weight_tensor(self, input_tensor):
    """Returns the weight tensor from the given transformed input_tensor."""
    return None

  # pylint: disable=unused-argument
  def _to_dnn_input_layer(self,
                          input_tensor,
                          weight_collections=None,
                          trainable=True,
                          output_rank=2):
    raise ValueError(
        "SparseColumn is not supported in DNN. "
        "Please use embedding_column or one_hot_column. column: {}".format(
            self))

  def _wide_embedding_lookup_arguments(self, input_tensor):
    return _LinearEmbeddingLookupArguments(
        input_tensor=self.id_tensor(input_tensor),
        weight_tensor=self.weight_tensor(input_tensor),
        vocab_size=self.length,
        initializer=init_ops.zeros_initializer(),
        combiner=self.combiner)

  def _get_input_sparse_tensor(self, columns_to_tensors):
    """Looks up the input tensor for transformation and sparsify it if dense."""
    input_tensor = columns_to_tensors[self.name]
    if not isinstance(input_tensor, sparse_tensor_py.SparseTensor):
      # To avoid making any assumptions about which values are to be ignored,
      # we set ignore_value to -1 for numeric tensors to avoid excluding valid
      # indices.
      if input_tensor.dtype == dtypes.string:
        ignore_value = ""
      else:
        ignore_value = -1
      input_tensor = _reshape_real_valued_tensor(input_tensor, 2, self.name)
      input_tensor = contrib_sparse_ops.dense_to_sparse_tensor(
          input_tensor, ignore_value=ignore_value)

    return input_tensor

  def is_compatible(self, other_column):
    """Check compatability of two sparse columns."""
    if self.lookup_config and other_column.lookup_config:
      return self.lookup_config == other_column.lookup_config
    compatible = (self.length == other_column.length and
                  (self.dtype == other_column.dtype or
                   (self.dtype.is_integer and other_column.dtype.is_integer)))
    if compatible:
      logging.warn("Column {} and {} may not have the same vocabulary.".
                   format(self.name, other_column.name))
    return compatible


class _SparseColumnIntegerized(_SparseColumn):
  """See `sparse_column_with_integerized_feature`."""

  def insert_transformed_feature(self, columns_to_tensors):
    """Handles sparse column to id conversion."""
    input_tensor = self._get_input_sparse_tensor(columns_to_tensors)

    sparse_id_values = math_ops.mod(input_tensor.values, self.bucket_size,
                                    name="mod")
    columns_to_tensors[self] = sparse_tensor_py.SparseTensor(
        input_tensor.indices, sparse_id_values, input_tensor.dense_shape)


def sparse_column_with_integerized_feature(column_name,
                                           bucket_size,
                                           combiner="sum",
                                           dtype=dtypes.int64):
  """Creates an integerized _SparseColumn.

  Use this when your features are already pre-integerized into int64 IDs, that
  is, when the set of values to output is already coming in as what's desired in
  the output. Integerized means we can use the feature value itself as id.

  Typically this is used for reading contiguous ranges of integers indexes, but
  it doesn't have to be. The output value is simply copied from the
  input_feature, whatever it is. Just be aware, however, that if you have large
  gaps of unused integers it might affect what you feed those in (for instance,
  if you make up a one-hot tensor from these, the unused integers will appear as
  values in the tensor which are always zero.)

  Args:
    column_name: A string defining sparse column name.
    bucket_size: An int that is > 1. The number of buckets. It should be bigger
      than maximum feature. In other words features in this column should be an
      int64 in range [0, bucket_size)
    combiner: A string specifying how to reduce if the sparse column is
      multivalent. Currently "mean", "sqrtn" and "sum" are supported, with "sum"
      the default. "sqrtn" often achieves good accuracy, in particular with
      bag-of-words columns.
        * "sum": do not normalize features in the column
        * "mean": do l1 normalization on features in the column
        * "sqrtn": do l2 normalization on features in the column
      For more information: `tf.embedding_lookup_sparse`.
    dtype: Type of features. It should be an integer type. Default value is
      dtypes.int64.

  Returns:
    An integerized _SparseColumn definition.

  Raises:
    ValueError: bucket_size is not greater than 1.
    ValueError: dtype is not integer.
  """
  return _SparseColumnIntegerized(
      column_name, is_integerized=True, bucket_size=bucket_size,
      combiner=combiner, dtype=dtype)


class _SparseColumnHashed(_SparseColumn):
  """See `sparse_column_with_hash_bucket`."""

  def insert_transformed_feature(self, columns_to_tensors):
    """Handles sparse column to id conversion."""
    input_tensor = self._get_input_sparse_tensor(columns_to_tensors)

    if self.dtype.is_integer:
      sparse_values = string_ops.as_string(input_tensor.values)
    else:
      sparse_values = input_tensor.values

    sparse_id_values = string_ops.string_to_hash_bucket_fast(
        sparse_values, self.bucket_size, name="lookup")
    columns_to_tensors[self] = sparse_tensor_py.SparseTensor(
        input_tensor.indices, sparse_id_values, input_tensor.dense_shape)


def sparse_column_with_hash_bucket(column_name,
                                   hash_bucket_size,
                                   combiner="sum",
                                   dtype=dtypes.string):
  """Creates a _SparseColumn with hashed bucket configuration.

  Use this when your sparse features are in string or integer format, but you
  don't have a vocab file that maps each value to an integer ID.
  output_id = Hash(input_feature_string) % bucket_size

  Args:
    column_name: A string defining sparse column name.
    hash_bucket_size: An int that is > 1. The number of buckets.
    combiner: A string specifying how to reduce if the sparse column is
      multivalent. Currently "mean", "sqrtn" and "sum" are supported, with "sum"
      the default. "sqrtn" often achieves good accuracy, in particular with
      bag-of-words columns.
        * "sum": do not normalize features in the column
        * "mean": do l1 normalization on features in the column
        * "sqrtn": do l2 normalization on features in the column
      For more information: `tf.embedding_lookup_sparse`.
    dtype: The type of features. Only string and integer types are supported.

  Returns:
    A _SparseColumn with hashed bucket configuration

  Raises:
    ValueError: hash_bucket_size is not greater than 2.
    ValueError: dtype is neither string nor integer.
  """
  return _SparseColumnHashed(
      column_name,
      bucket_size=hash_bucket_size,
      combiner=combiner,
      dtype=dtype)


class _SparseColumnKeys(_SparseColumn):
  """See `sparse_column_with_keys`."""

  def insert_transformed_feature(self, columns_to_tensors):
    """Handles sparse column to id conversion."""
    input_tensor = self._get_input_sparse_tensor(columns_to_tensors)

    table = lookup.index_table_from_tensor(
        mapping=tuple(self.lookup_config.keys),
        default_value=self.lookup_config.default_value,
        dtype=self.dtype,
        name="lookup")
    columns_to_tensors[self] = table.lookup(input_tensor)


def sparse_column_with_keys(
    column_name, keys, default_value=-1, combiner="sum", dtype=dtypes.string):
  """Creates a _SparseColumn with keys.

  Look up logic is as follows:
  lookup_id = index_of_feature_in_keys if feature in keys else default_value

  Args:
    column_name: A string defining sparse column name.
    keys: A list or tuple defining vocabulary. Must be castable to `dtype`.
    default_value: The value to use for out-of-vocabulary feature values.
      Default is -1.
    combiner: A string specifying how to reduce if the sparse column is
      multivalent. Currently "mean", "sqrtn" and "sum" are supported, with "sum"
      the default. "sqrtn" often achieves good accuracy, in particular with
      bag-of-words columns.
        * "sum": do not normalize features in the column
        * "mean": do l1 normalization on features in the column
        * "sqrtn": do l2 normalization on features in the column
      For more information: `tf.embedding_lookup_sparse`.
    dtype: Type of features. Only integer and string are supported.

  Returns:
    A _SparseColumnKeys with keys configuration.
  """
  keys = tuple(keys)
  return _SparseColumnKeys(
      column_name,
      lookup_config=_SparseIdLookupConfig(
          keys=keys, vocab_size=len(keys), default_value=default_value),
      combiner=combiner,
      dtype=dtype)


class _SparseColumnVocabulary(_SparseColumn):
  """See `sparse_column_with_vocabulary_file`."""

  def insert_transformed_feature(self, columns_to_tensors):
    """Handles sparse column to id conversion."""
    st = self._get_input_sparse_tensor(columns_to_tensors)
    if self.dtype.is_integer:
      sparse_string_values = string_ops.as_string(st.values)
      sparse_string_tensor = sparse_tensor_py.SparseTensor(st.indices,
                                                           sparse_string_values,
                                                           st.dense_shape)
    else:
      sparse_string_tensor = st

    table = lookup.string_to_index_table_from_file(
        vocabulary_file=self.lookup_config.vocabulary_file,
        num_oov_buckets=self.lookup_config.num_oov_buckets,
        vocab_size=self.lookup_config.vocab_size,
        default_value=self.lookup_config.default_value,
        name=self.name + "_lookup")
    columns_to_tensors[self] = table.lookup(sparse_string_tensor)


def sparse_column_with_vocabulary_file(column_name,
                                       vocabulary_file,
                                       num_oov_buckets=0,
                                       vocab_size=None,
                                       default_value=-1,
                                       combiner="sum",
                                       dtype=dtypes.string):
  """Creates a _SparseColumn with vocabulary file configuration.

  Use this when your sparse features are in string or integer format, and you
  have a vocab file that maps each value to an integer ID.
  output_id = LookupIdFromVocab(input_feature_string)

  Args:
    column_name: A string defining sparse column name.
    vocabulary_file: The vocabulary filename.
    num_oov_buckets: The number of out-of-vocabulary buckets. If zero all out of
      vocabulary features will be ignored.
    vocab_size: Number of the elements in the vocabulary.
    default_value: The value to use for out-of-vocabulary feature values.
      Defaults to -1.
    combiner: A string specifying how to reduce if the sparse column is
      multivalent. Currently "mean", "sqrtn" and "sum" are supported, with "sum"
      the default. "sqrtn" often achieves good accuracy, in particular with
      bag-of-words columns.
        * "sum": do not normalize features in the column
        * "mean": do l1 normalization on features in the column
        * "sqrtn": do l2 normalization on features in the column
      For more information: `tf.embedding_lookup_sparse`.
    dtype: The type of features. Only string and integer types are supported.

  Returns:
    A _SparseColumn with vocabulary file configuration.

  Raises:
    ValueError: vocab_size is not defined.
    ValueError: dtype is neither string nor integer.
  """
  if vocab_size is None:
    raise ValueError("vocab_size should be defined. "
                     "column_name: {}".format(column_name))

  return _SparseColumnVocabulary(
      column_name,
      lookup_config=_SparseIdLookupConfig(
          vocabulary_file=vocabulary_file,
          num_oov_buckets=num_oov_buckets,
          vocab_size=vocab_size,
          default_value=default_value),
      combiner=combiner,
      dtype=dtype)


class _WeightedSparseColumn(_FeatureColumn, collections.namedtuple(
    "_WeightedSparseColumn",
    ["sparse_id_column", "weight_column_name", "dtype"])):
  """See `weighted_sparse_column`."""

  def __new__(cls, sparse_id_column, weight_column_name, dtype):
    return super(_WeightedSparseColumn, cls).__new__(cls, sparse_id_column,
                                                     weight_column_name, dtype)

  @property
  def name(self):
    return "{}_weighted_by_{}".format(self.sparse_id_column.name,
                                      self.weight_column_name)

  @property
  def length(self):
    """Returns id size."""
    return self.sparse_id_column.length

  @property
  def config(self):
    config = _get_feature_config(self.sparse_id_column)
    config.update(
        {self.weight_column_name: parsing_ops.VarLenFeature(self.dtype)})
    return config

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return "{}".format(self)

  def insert_transformed_feature(self, columns_to_tensors):
    """Inserts a tuple with the id and weight tensors."""
    if self.sparse_id_column not in columns_to_tensors:
      self.sparse_id_column.insert_transformed_feature(columns_to_tensors)

    weight_tensor = columns_to_tensors[self.weight_column_name]
    if not isinstance(weight_tensor, sparse_tensor_py.SparseTensor):
      # The weight tensor can be a regular Tensor. In such case, sparsify it.
      weight_tensor = contrib_sparse_ops.dense_to_sparse_tensor(weight_tensor)
    if not self.dtype.is_floating:
      weight_tensor = math_ops.to_float(weight_tensor)
    columns_to_tensors[self] = tuple([
        columns_to_tensors[self.sparse_id_column],
        weight_tensor
    ])

  def id_tensor(self, input_tensor):
    """Returns the id tensor from the given transformed input_tensor."""
    return input_tensor[0]

  def weight_tensor(self, input_tensor):
    """Returns the weight tensor from the given transformed input_tensor."""
    return input_tensor[1]

  # pylint: disable=unused-argument
  def _to_dnn_input_layer(self,
                          input_tensor,
                          weight_collections=None,
                          trainable=True,
                          output_rank=2):
    raise ValueError(
        "WeightedSparseColumn is not supported in DNN. "
        "Please use embedding_column or one_hot_column. column: {}".format(
            self))

  def _wide_embedding_lookup_arguments(self, input_tensor):
    return _LinearEmbeddingLookupArguments(
        input_tensor=self.id_tensor(input_tensor),
        weight_tensor=self.weight_tensor(input_tensor),
        vocab_size=self.length,
        initializer=init_ops.zeros_initializer(),
        combiner=self.sparse_id_column.combiner)


def weighted_sparse_column(sparse_id_column,
                           weight_column_name,
                           dtype=dtypes.float32):
  """Creates a _SparseColumn by combining sparse_id_column with a weight column.

  Example:

    ```python
    sparse_feature = sparse_column_with_hash_bucket(column_name="sparse_col",
                                                    hash_bucket_size=1000)
    weighted_feature = weighted_sparse_column(sparse_id_column=sparse_feature,
                                              weight_column_name="weights_col")
    ```

    This configuration assumes that input dictionary of model contains the
    following two items:
      * (key="sparse_col", value=sparse_tensor) where sparse_tensor is
        a SparseTensor.
      * (key="weights_col", value=weights_tensor) where weights_tensor
        is a SparseTensor.
     Following are assumed to be true:
       * sparse_tensor.indices = weights_tensor.indices
       * sparse_tensor.dense_shape = weights_tensor.dense_shape

  Args:
    sparse_id_column: A `_SparseColumn` which is created by
      `sparse_column_with_*` functions.
    weight_column_name: A string defining a sparse column name which represents
      weight or value of the corresponding sparse id feature.
    dtype: Type of weights, such as `tf.float32`. Only floating and integer
      weights are supported.
  Returns:
    A _WeightedSparseColumn composed of two sparse features: one represents id,
    the other represents weight (value) of the id feature in that example.
  Raises:
    ValueError: if dtype is not convertible to float.
  """
  if not (dtype.is_integer or dtype.is_floating):
    raise ValueError("dtype is not convertible to float. Given {}".format(
        dtype))

  return _WeightedSparseColumn(sparse_id_column, weight_column_name, dtype)


class _OneHotColumn(_FeatureColumn,
                    collections.namedtuple("_OneHotColumn",
                                           ["sparse_id_column"])):
  """Represents a one-hot column for use in deep networks.

  Args:
    sparse_id_column: A _SparseColumn which is created by `sparse_column_with_*`
      function.
  """

  @property
  def name(self):
    return "{}_one_hot".format(self.sparse_id_column.name)

  @property
  def length(self):
    """Returns vocabulary or hash_bucket size."""
    return self.sparse_id_column.length

  @property
  def config(self):
    """Returns the parsing config of the origin column."""
    return _get_feature_config(self.sparse_id_column)

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return "{}".format(self)

  def insert_transformed_feature(self, columns_to_tensors):
    """Used by the Transformer to prevent double transformations."""
    if self.sparse_id_column not in columns_to_tensors:
      self.sparse_id_column.insert_transformed_feature(columns_to_tensors)
    columns_to_tensors[self] = columns_to_tensors[self.sparse_id_column]

  def _to_dnn_input_layer(self,
                          transformed_input_tensor,
                          unused_weight_collections=None,
                          unused_trainable=False,
                          output_rank=2):
    """Returns a Tensor as an input to the first layer of neural network.

    Args:
      transformed_input_tensor: A tensor that has undergone the transformations
      in `insert_transformed_feature`. Rank should be >= `output_rank`.
      unused_weight_collections: Unused. One hot encodings are not variable.
      unused_trainable: Unused. One hot encodings are not trainable.
      output_rank: the desired rank of the output `Tensor`.

    Returns:
      A multihot Tensor to be fed into the first layer of neural network.

    Raises:
      ValueError: When using one_hot_column with weighted_sparse_column.
      This is not yet supported.
    """

    # Reshape ID column to `output_rank`.
    sparse_id_column = self.sparse_id_column.id_tensor(transformed_input_tensor)
    # pylint: disable=protected-access
    sparse_id_column = layers._inner_flatten(sparse_id_column, output_rank)

    weight_tensor = self.sparse_id_column.weight_tensor(
        transformed_input_tensor)
    if weight_tensor is not None:
      weighted_column = sparse_ops.sparse_merge(sp_ids=sparse_id_column,
                                                sp_values=weight_tensor,
                                                vocab_size=self.length)
      return sparse_ops.sparse_tensor_to_dense(weighted_column)

    dense_id_tensor = sparse_ops.sparse_tensor_to_dense(sparse_id_column,
                                                        default_value=-1)

    # One hot must be float for tf.concat reasons since all other inputs to
    # input_layer are float32.
    one_hot_id_tensor = array_ops.one_hot(
        dense_id_tensor, depth=self.length, on_value=1.0, off_value=0.0)

    # Reduce to get a multi-hot per example.
    return math_ops.reduce_sum(
        one_hot_id_tensor, reduction_indices=[output_rank - 1])


class _EmbeddingColumn(_FeatureColumn, collections.namedtuple(
    "_EmbeddingColumn",
    ["sparse_id_column", "dimension", "combiner", "initializer",
     "ckpt_to_load_from", "tensor_name_in_ckpt", "shared_embedding_name",
     "shared_vocab_size", "max_norm", "trainable"])):
  """Represents an embedding column.

  Args:
    sparse_id_column: A `_SparseColumn` which is created by
      `sparse_column_with_*` or `weighted_sparse_column` functions.
    dimension: An integer specifying dimension of the embedding.
    combiner: A string specifying how to reduce if there are multiple entries
      in a single row. Currently "mean", "sqrtn" and "sum" are supported, with
      "mean" the default. "sqrtn" often achieves good accuracy, in particular
      with bag-of-words columns. Each of this can be thought as example level
      normalizations on the column:
        * "sum": do not normalize features in the column
        * "mean": do l1 normalization on features in the column
        * "sqrtn": do l2 normalization on features in the column
      For more information: `tf.embedding_lookup_sparse`.
    initializer: A variable initializer function to be used in embedding
      variable initialization. If not specified, defaults to
      `tf.truncated_normal_initializer` with mean 0.0 and standard deviation
      1/sqrt(sparse_id_column.length).
    ckpt_to_load_from: (Optional). String representing checkpoint name/pattern
      to restore the column weights. Required if `tensor_name_in_ckpt` is not
      None.
    tensor_name_in_ckpt: (Optional). Name of the `Tensor` in the provided
      checkpoint from which to restore the column weights. Required if
      `ckpt_to_load_from` is not None.
    shared_embedding_name: (Optional). The common name for shared embedding.
    shared_vocab_size: (Optional). The common vocab_size used for shared
      embedding space.
    max_norm: (Optional). If not None, embedding values are l2-normalized to
      the value of max_norm.
    trainable: (Optional). Should the embedding be trainable. Default is True.

  Raises:
    ValueError: if `initializer` is specified and is not callable. Also,
      if only one of `ckpt_to_load_from` and `tensor_name_in_ckpt` is specified.
  """

  def __new__(cls,
              sparse_id_column,
              dimension,
              combiner="mean",
              initializer=None,
              ckpt_to_load_from=None,
              tensor_name_in_ckpt=None,
              shared_embedding_name=None,
              shared_vocab_size=None,
              max_norm=None,
              trainable=True):
    if initializer is not None and not callable(initializer):
      raise ValueError("initializer must be callable if specified. "
                       "Embedding of column_name: {}".format(
                           sparse_id_column.name))

    if (ckpt_to_load_from is None) != (tensor_name_in_ckpt is None):
      raise ValueError("Must specify both `ckpt_to_load_from` and "
                       "`tensor_name_in_ckpt` or none of them.")
    if initializer is None:
      logging.warn("The default stddev value of initializer will change from "
                   "\"1/sqrt(vocab_size)\" to \"1/sqrt(dimension)\" after "
                   "2017/02/25.")
      stddev = 1 / math.sqrt(sparse_id_column.length)
      initializer = init_ops.truncated_normal_initializer(
          mean=0.0, stddev=stddev)
    return super(_EmbeddingColumn, cls).__new__(cls, sparse_id_column,
                                                dimension, combiner,
                                                initializer, ckpt_to_load_from,
                                                tensor_name_in_ckpt,
                                                shared_embedding_name,
                                                shared_vocab_size,
                                                max_norm,
                                                trainable)

  @property
  def name(self):
    if self.shared_embedding_name is None:
      return "{}_embedding".format(self.sparse_id_column.name)
    else:
      return "{}_shared_embedding".format(self.sparse_id_column.name)

  @property
  def length(self):
    """Returns id size."""
    if self.shared_vocab_size is None:
      return self.sparse_id_column.length
    else:
      return self.shared_vocab_size

  @property
  def config(self):
    return _get_feature_config(self.sparse_id_column)

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return self._key_without_properties(["initializer"])

  def insert_transformed_feature(self, columns_to_tensors):
    if self.sparse_id_column not in columns_to_tensors:
      self.sparse_id_column.insert_transformed_feature(columns_to_tensors)
    columns_to_tensors[self] = columns_to_tensors[self.sparse_id_column]

  def _deep_embedding_lookup_arguments(self, input_tensor):
    return _DeepEmbeddingLookupArguments(
        input_tensor=self.sparse_id_column.id_tensor(input_tensor),
        weight_tensor=self.sparse_id_column.weight_tensor(input_tensor),
        vocab_size=self.length,
        dimension=self.dimension,
        initializer=self.initializer,
        combiner=self.combiner,
        shared_embedding_name=self.shared_embedding_name,
        hash_key=None,
        max_norm=self.max_norm,
        trainable=self.trainable)

  def _checkpoint_path(self):
    if self.ckpt_to_load_from is not None:
      return self.ckpt_to_load_from, self.tensor_name_in_ckpt
    return None

  # pylint: disable=unused-argument
  def _wide_embedding_lookup_arguments(self, input_tensor):
    raise ValueError("Column {} is not supported in linear models. "
                     "Please use sparse_column.".format(self))


def one_hot_column(sparse_id_column):
  """Creates an `_OneHotColumn` for a one-hot or multi-hot repr in a DNN.

  Args:
      sparse_id_column: A _SparseColumn which is created by
        `sparse_column_with_*`
        or crossed_column functions. Note that `combiner` defined in
        `sparse_id_column` is ignored.

  Returns:
    An _OneHotColumn.
  """
  return _OneHotColumn(sparse_id_column)


def embedding_column(sparse_id_column,
                     dimension,
                     combiner="mean",
                     initializer=None,
                     ckpt_to_load_from=None,
                     tensor_name_in_ckpt=None,
                     max_norm=None,
                     trainable=True):
  """Creates an `_EmbeddingColumn` for feeding sparse data into a DNN.

  Args:
    sparse_id_column: A `_SparseColumn` which is created by for example
      `sparse_column_with_*` or crossed_column functions. Note that `combiner`
      defined in `sparse_id_column` is ignored.
    dimension: An integer specifying dimension of the embedding.
    combiner: A string specifying how to reduce if there are multiple entries
      in a single row. Currently "mean", "sqrtn" and "sum" are supported, with
      "mean" the default. "sqrtn" often achieves good accuracy, in particular
      with bag-of-words columns. Each of this can be thought as example level
      normalizations on the column:
        * "sum": do not normalize
        * "mean": do l1 normalization
        * "sqrtn": do l2 normalization
      For more information: `tf.embedding_lookup_sparse`.
    initializer: A variable initializer function to be used in embedding
      variable initialization. If not specified, defaults to
      `tf.truncated_normal_initializer` with mean 0.0 and standard deviation
      1/sqrt(sparse_id_column.length).
    ckpt_to_load_from: (Optional). String representing checkpoint name/pattern
      to restore the column weights. Required if `tensor_name_in_ckpt` is not
      None.
    tensor_name_in_ckpt: (Optional). Name of the `Tensor` in the provided
      checkpoint from which to restore the column weights. Required if
      `ckpt_to_load_from` is not None.
    max_norm: (Optional). If not None, embedding values are l2-normalized to
      the value of max_norm.
    trainable: (Optional). Should the embedding be trainable. Default is True

  Returns:
    An `_EmbeddingColumn`.
  """
  return _EmbeddingColumn(sparse_id_column, dimension, combiner, initializer,
                          ckpt_to_load_from, tensor_name_in_ckpt,
                          max_norm=max_norm, trainable=trainable)


def shared_embedding_columns(sparse_id_columns,
                             dimension,
                             combiner="mean",
                             shared_embedding_name=None,
                             initializer=None,
                             ckpt_to_load_from=None,
                             tensor_name_in_ckpt=None,
                             max_norm=None,
                             trainable=True):
  """Creates a list of `_EmbeddingColumn` sharing the same embedding.

  Args:
    sparse_id_columns: An iterable of `_SparseColumn`, such as those created by
      `sparse_column_with_*` or crossed_column functions. Note that `combiner`
      defined in each sparse_id_column is ignored.
    dimension: An integer specifying dimension of the embedding.
    combiner: A string specifying how to reduce if there are multiple entries
      in a single row. Currently "mean", "sqrtn" and "sum" are supported, with
      "mean" the default. "sqrtn" often achieves good accuracy, in particular
      with bag-of-words columns. Each of this can be thought as example level
      normalizations on the column:
        * "sum": do not normalize
        * "mean": do l1 normalization
        * "sqrtn": do l2 normalization
      For more information: `tf.embedding_lookup_sparse`.
    shared_embedding_name: (Optional). A string specifying the name of shared
      embedding weights. This will be needed if you want to reference the shared
      embedding separately from the generated `_EmbeddingColumn`.
    initializer: A variable initializer function to be used in embedding
      variable initialization. If not specified, defaults to
      `tf.truncated_normal_initializer` with mean 0.0 and standard deviation
      1/sqrt(sparse_id_columns[0].length).
    ckpt_to_load_from: (Optional). String representing checkpoint name/pattern
      to restore the column weights. Required if `tensor_name_in_ckpt` is not
      None.
    tensor_name_in_ckpt: (Optional). Name of the `Tensor` in the provided
      checkpoint from which to restore the column weights. Required if
      `ckpt_to_load_from` is not None.
    max_norm: (Optional). If not None, embedding values are l2-normalized to
      the value of max_norm.
    trainable: (Optional). Should the embedding be trainable. Default is True

  Returns:
    A tuple of `_EmbeddingColumn` with shared embedding space.

  Raises:
    ValueError: if sparse_id_columns is empty, or its elements are not
      compatible with each other.
    TypeError: if `sparse_id_columns` is not a sequence or is a string. If at
      least one element of `sparse_id_columns` is not a `SparseTensor`.
  """
  if (not isinstance(sparse_id_columns, collections.Sequence) or
      isinstance(sparse_id_columns, six.string_types)):
    raise TypeError(
        "sparse_id_columns must be a non-string sequence (ex: list or tuple) "
        "instead of type {}.".format(type(sparse_id_columns)))
  if len(sparse_id_columns) < 1:
    raise ValueError("The input sparse_id_columns should have at least one "
                     "element.")
  for sparse_id_column in sparse_id_columns:
    if not isinstance(sparse_id_column, _SparseColumn):
      raise TypeError("Elements of sparse_id_columns must be _SparseColumn, but"
                      "{} is not.".format(sparse_id_column))

  if len(sparse_id_columns) == 1:
    return [
        _EmbeddingColumn(sparse_id_columns[0], dimension, combiner, initializer,
                         ckpt_to_load_from, tensor_name_in_ckpt,
                         shared_embedding_name, max_norm=max_norm,
                         trainable=trainable)]
  else:
    # check compatibility of sparse_id_columns
    compatible = True
    for column in sparse_id_columns[1:]:
      compatible = compatible and column.is_compatible(sparse_id_columns[0])
    if not compatible:
      raise ValueError("The input sparse id columns are not compatible.")
    # Construct the shared name and size for shared embedding space.
    if not shared_embedding_name:
      # Sort the columns so that shared_embedding_name will be deterministic
      # even if users pass in unsorted columns from a dict or something.
      sorted_columns = sorted(sparse_id_columns)
      if len(sorted_columns) <= 3:
        shared_embedding_name = "_".join([column.name
                                          for column in sorted_columns])
      else:
        shared_embedding_name = "_".join([column.name
                                          for column in sorted_columns[0:3]])
        shared_embedding_name += (
            "_plus_{}_others".format(len(sorted_columns) - 3))
      shared_embedding_name += "_shared_embedding"
    shared_vocab_size = sparse_id_columns[0].length

    embedded_columns = []
    for column in sparse_id_columns:
      embedded_columns.append(
          _EmbeddingColumn(column, dimension, combiner, initializer,
                           ckpt_to_load_from, tensor_name_in_ckpt,
                           shared_embedding_name, shared_vocab_size,
                           max_norm=max_norm, trainable=trainable))
    return tuple(embedded_columns)


class _ScatteredEmbeddingColumn(
    _FeatureColumn,
    collections.namedtuple(
        "_ScatteredEmbeddingColumn",
        ["column_name", "size", "dimension", "hash_key", "combiner",
         "initializer"])):
  """See `scattered_embedding_column`."""

  def __new__(cls,
              column_name,
              size,
              dimension,
              hash_key,
              combiner="sqrtn",
              initializer=None):
    if initializer is not None and not callable(initializer):
      raise ValueError("initializer must be callable if specified. "
                       "column_name: {}".format(column_name))
    if initializer is None:
      logging.warn("The default stddev value of initializer will change from "
                   "\"0.1\" to \"1/sqrt(dimension)\" after 2017/02/25.")
      stddev = 0.1
      initializer = init_ops.truncated_normal_initializer(
          mean=0.0, stddev=stddev)
    return super(_ScatteredEmbeddingColumn, cls).__new__(cls, column_name, size,
                                                         dimension, hash_key,
                                                         combiner,
                                                         initializer)

  @property
  def name(self):
    return "{}_scattered_embedding".format(self.column_name)

  @property
  def config(self):
    return {self.column_name: parsing_ops.VarLenFeature(dtypes.string)}

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return self._key_without_properties(["initializer"])

  def insert_transformed_feature(self, columns_to_tensors):
    columns_to_tensors[self] = columns_to_tensors[self.column_name]

  def _deep_embedding_lookup_arguments(self, input_tensor):
    return _DeepEmbeddingLookupArguments(
        input_tensor=input_tensor,
        weight_tensor=None,
        vocab_size=self.size,
        initializer=self.initializer,
        combiner=self.combiner,
        dimension=self.dimension,
        shared_embedding_name=None,
        hash_key=self.hash_key,
        max_norm=None,
        trainable=True)


def scattered_embedding_column(column_name,
                               size,
                               dimension,
                               hash_key,
                               combiner="mean",
                               initializer=None):
  """Creates an embedding column of a sparse feature using parameter hashing.

  This is a useful shorthand when you have a sparse feature you want to use an
  embedding for, but also want to hash the embedding's values in each dimension
  to a variable based on a different hash.

  Specifically, the i-th embedding component of a value v is found by retrieving
  an embedding weight whose index is a fingerprint of the pair (v,i).

  An embedding column with sparse_column_with_hash_bucket such as

      embedding_column(
        sparse_column_with_hash_bucket(column_name, bucket_size),
        dimension)

  could be replaced by

      scattered_embedding_column(
        column_name,
        size=bucket_size * dimension,
        dimension=dimension,
        hash_key=tf.contrib.layers.SPARSE_FEATURE_CROSS_DEFAULT_HASH_KEY)

  for the same number of embedding parameters. This should hopefully reduce the
  impact of collisions, but adds the cost of slowing down training.

  Args:
    column_name: A string defining sparse column name.
    size: An integer specifying the number of parameters in the embedding layer.
    dimension: An integer specifying dimension of the embedding.
    hash_key: Specify the hash_key that will be used by the `FingerprintCat64`
      function to combine the crosses fingerprints on SparseFeatureCrossOp.
    combiner: A string specifying how to reduce if there are multiple entries
      in a single row. Currently "mean", "sqrtn" and "sum" are supported, with
      "mean" the default. "sqrtn" often achieves good accuracy, in particular
      with bag-of-words columns. Each of this can be thought as example level
      normalizations on the column:
        * "sum": do not normalize features in the column
        * "mean": do l1 normalization on features in the column
        * "sqrtn": do l2 normalization on features in the column
      For more information: `tf.embedding_lookup_sparse`.
    initializer: A variable initializer function to be used in embedding
      variable initialization. If not specified, defaults to
      `tf.truncated_normal_initializer` with mean 0 and standard deviation 0.1.

  Returns:
    A _ScatteredEmbeddingColumn.

  Raises:
    ValueError: if dimension or size is not a positive integer; or if combiner
      is not supported.

  """
  if (dimension < 1) or (size < 1):
    raise ValueError("Dimension and size must be greater than 0. "
                     "dimension: {}, size: {}, column_name: {}".format(
                         dimension, size, column_name))

  if combiner not in ("mean", "sqrtn", "sum"):
    raise ValueError("Combiner must be one of 'mean', 'sqrtn' or 'sum'. "
                     "combiner: {}, column_name: {}".format(combiner,
                                                            column_name))

  return _ScatteredEmbeddingColumn(column_name, size, dimension, hash_key,
                                   combiner, initializer)


def _reshape_real_valued_tensor(input_tensor, output_rank, column_name=None):
  """Reshaping logic for dense, numeric `Tensors`.

  Follows the following rules:
    1. If `output_rank > input_rank + 1` raise a `ValueError`.
    2. If `output_rank == input_rank + 1`, expand `input_tensor` by one
       dimension and return
    3. If `output_rank == input_rank`, return `input_tensor`.
    4. If `output_rank < input_rank`, flatten the inner dimensions of
       `input_tensor` and return a `Tensor` with `output_rank`

  Args:
    input_tensor: a dense `Tensor` to be reshaped.
    output_rank: the desired rank of the reshaped `Tensor`.
    column_name: (optional) the name of the associated column. Used for error
      messages.
  Returns:
    A `Tensor` with the same entries as `input_tensor` and rank `output_rank`.
  Raises:
    ValueError: if `output_rank > input_rank + 1`.
  """
  input_rank = input_tensor.get_shape().ndims
  if input_rank is not None:
    if output_rank > input_rank + 1:
      error_string = ("Rank of input Tensor ({}) should be the same as "
                      "output_rank ({}). For example, sequence data should "
                      "typically be 3 dimensional (rank 3) while non-sequence "
                      "data is typically 2 dimensional (rank 2).".format(
                          input_rank, output_rank))
      if column_name is not None:
        error_string = ("Error while processing column {}.".format(column_name)
                        + error_string)
      raise ValueError(error_string)
    if output_rank == input_rank + 1:
      logging.warning(
          "Rank of input Tensor ({}) should be the same as output_rank ({}) "
          "for column. Will attempt to expand dims. It is highly recommended "
          "that you resize your input, as this behavior may change.".format(
              input_rank, output_rank))
      return array_ops.expand_dims(input_tensor, -1, name="expand_dims")
    if output_rank == input_rank:
      return input_tensor
  # Here, either `input_rank` is unknown or it is greater than `output_rank`.
  return layers._inner_flatten(input_tensor, output_rank)  # pylint: disable=protected-access


class _RealValuedColumn(_FeatureColumn, collections.namedtuple(
    "_RealValuedColumn",
    ["column_name", "dimension", "default_value", "dtype", "normalizer"])):
  """Represents a real valued feature column also known as continuous features.

  Instances of this class are immutable. A real valued column with a specified
  dimension means features are dense, otherwise they're sparse.
  In the dense case, the dictionary returned by InputBuilder contains a
  ("column_name", Tensor) pair with a Tensor shape of (batch_size, dimension).
  In the sparse shape, the dictionary contains a ("column_name", SparseTensor)
  pair instead with shape inferred after parsing.
  """

  def __new__(cls, column_name, dimension, default_value,
              dtype, normalizer):
    if default_value is not None:
      default_value = tuple(default_value)
    return super(_RealValuedColumn, cls).__new__(cls, column_name, dimension,
                                                 default_value, dtype,
                                                 normalizer)

  @property
  def name(self):
    return self.column_name

  @property
  def config(self):
    if self.dimension is None:
      return {self.column_name: parsing_ops.VarLenFeature(self.dtype)}
    else:
      default_value = self.default_value
      if default_value is not None:
        default_value = list(default_value)
      return {self.column_name: parsing_ops.FixedLenFeature([self.dimension],
                                                            self.dtype,
                                                            default_value)}

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return self._key_without_properties(["normalizer"])

  @property
  def normalizer_fn(self):
    """Returns the function used to normalize the column."""
    return self.normalizer

  def _normalized_input_tensor(self, input_tensor):
    """Returns the input tensor after custom normalization is applied."""
    return (self.normalizer(input_tensor) if self.normalizer is not None else
            input_tensor)

  def insert_transformed_feature(self, columns_to_tensors):
    """Apply transformation and inserts it into columns_to_tensors.

    Args:
      columns_to_tensors: A mapping from feature columns to tensors. 'string'
        key means a base feature (not-transformed). It can have _FeatureColumn
        as a key too. That means that _FeatureColumn is already transformed.
    """
    # Transform the input tensor according to the normalizer function.
    input_tensor = self._normalized_input_tensor(columns_to_tensors[self.name])
    columns_to_tensors[self] = math_ops.to_float(input_tensor)

  # pylint: disable=unused-argument
  def _to_dnn_input_layer(self,
                          input_tensor,
                          weight_collections=None,
                          trainable=True,
                          output_rank=2):
    input_tensor = self._to_dense_tensor(input_tensor)
    if input_tensor.dtype != dtypes.float32:
      input_tensor = math_ops.to_float(input_tensor)
    return _reshape_real_valued_tensor(input_tensor, output_rank, self.name)

  def _to_dense_tensor(self, input_tensor):
    if isinstance(input_tensor, sparse_tensor_py.SparseTensor):
      default_value = (self.default_value[0] if self.default_value is not None
                       else 0)
      return sparse_ops.sparse_tensor_to_dense(
          input_tensor, default_value=default_value)
    return input_tensor


def real_valued_column(column_name,
                       dimension=1,
                       default_value=None,
                       dtype=dtypes.float32,
                       normalizer=None):
  """Creates a `_RealValuedColumn` for dense numeric data.

  Args:
    column_name: A string defining real valued column name.
    dimension: An integer specifying dimension of the real valued column.
      The default is 1. When dimension is not None, the Tensor representing
      the _RealValuedColumn will have the shape of [batch_size, dimension].
      A None dimension means the feature column should be treat as variable
      length and will be parsed as a `SparseTensor`.
    default_value: A single value compatible with dtype or a list of values
      compatible with dtype which the column takes on during tf.Example parsing
      if data is missing. When dimension is not None, a default value of None
      will cause tf.parse_example to fail if an example does not contain this
      column. If a single value is provided, the same value will be applied as
      the default value for every dimension. If a list of values is provided,
      the length of the list should be equal to the value of `dimension`.
      Only scalar default value is supported in case dimension is not specified.
    dtype: defines the type of values. Default value is tf.float32. Must be a
      non-quantized, real integer or floating point type.
    normalizer: If not None, a function that can be used to normalize the value
      of the real valued column after default_value is applied for parsing.
      Normalizer function takes the input tensor as its argument, and returns
      the output tensor. (e.g. lambda x: (x - 3.0) / 4.2). Note that for
      variable length columns, the normalizer should expect an input_tensor of
      type `SparseTensor`.
  Returns:
    A _RealValuedColumn.
  Raises:
    TypeError: if dimension is not an int
    ValueError: if dimension is not a positive integer
    TypeError: if default_value is a list but its length is not equal to the
      value of `dimension`.
    TypeError: if default_value is not compatible with dtype.
    ValueError: if dtype is not convertible to tf.float32.
  """

  if dimension is not None:
    if not isinstance(dimension, int):
      raise TypeError("dimension must be an integer. "
                      "dimension: {}, column_name: {}".format(dimension,
                                                              column_name))
    if dimension < 1:
      raise ValueError("dimension must be greater than 0. "
                       "dimension: {}, column_name: {}".format(dimension,
                                                               column_name))

  if not (dtype.is_integer or dtype.is_floating):
    raise ValueError("dtype must be convertible to float. "
                     "dtype: {}, column_name: {}".format(dtype, column_name))

  if default_value is None:
    return _RealValuedColumn(column_name, dimension, default_value, dtype,
                             normalizer)

  if isinstance(default_value, int):
    if dtype.is_integer:
      default_value = ([default_value for _ in range(dimension)] if dimension
                       else [default_value])
      return _RealValuedColumn(column_name, dimension, default_value, dtype,
                               normalizer)
    if dtype.is_floating:
      default_value = float(default_value)
      default_value = ([default_value for _ in range(dimension)] if dimension
                       else [default_value])
      return _RealValuedColumn(column_name, dimension, default_value, dtype,
                               normalizer)

  if isinstance(default_value, float):
    if dtype.is_floating and (not dtype.is_integer):
      default_value = ([default_value for _ in range(dimension)] if dimension
                       else [default_value])
      return _RealValuedColumn(column_name, dimension, default_value, dtype,
                               normalizer)

  if isinstance(default_value, list):
    if dimension is None:
      raise ValueError(
          "Only scalar default value is supported when dimension is None. "
          "default_value: {}, column_name: {}".format(
              default_value, column_name))
    if len(default_value) != dimension:
      raise ValueError(
          "The length of default_value must be equal to dimension. "
          "default_value: {}, dimension: {}, column_name: {}".format(
              default_value, dimension, column_name))
    # Check if the values in the list are all integers or are convertible to
    # floats.
    is_list_all_int = True
    is_list_all_float = True
    for v in default_value:
      if not isinstance(v, int):
        is_list_all_int = False
      if not (isinstance(v, float) or isinstance(v, int)):
        is_list_all_float = False
    if is_list_all_int:
      if dtype.is_integer:
        return _RealValuedColumn(column_name, dimension, default_value, dtype,
                                 normalizer)
      elif dtype.is_floating:
        default_value = [float(v) for v in default_value]
        return _RealValuedColumn(column_name, dimension, default_value, dtype,
                                 normalizer)
    if is_list_all_float:
      if dtype.is_floating and (not dtype.is_integer):
        default_value = [float(v) for v in default_value]
        return _RealValuedColumn(column_name, dimension, default_value, dtype,
                                 normalizer)

  raise TypeError("default_value must be compatible with dtype. "
                  "default_value: {}, dtype: {}, column_name: {}".format(
                      default_value, dtype, column_name))


class _BucketizedColumn(_FeatureColumn, collections.namedtuple(
    "_BucketizedColumn", ["source_column", "boundaries"])):
  """Represents a bucketization transformation also known as binning.

  Instances of this class are immutable. Values in `source_column` will be
  bucketized based on `boundaries`.
  For example, if the inputs are:
      boundaries = [0, 10, 100]
      source_column = [[-5], [150], [10], [0], [4], [19]]

  then the bucketized feature will be:
      output = [[0], [3], [2], [1], [1], [2]]

  Attributes:
    source_column: A _RealValuedColumn defining dense column.
    boundaries: A list or tuple of floats specifying the boundaries. It has to
      be sorted. [a, b, c] defines following buckets: (-inf., a), [a, b),
      [b, c), [c, inf.)
  Raises:
    ValueError: if 'boundaries' is empty or not sorted.
  """

  def __new__(cls, source_column, boundaries):
    if not isinstance(source_column, _RealValuedColumn):
      raise TypeError("source_column must be an instance of _RealValuedColumn. "
                      "source_column: {}".format(source_column))

    if source_column.dimension is None:
      raise ValueError("source_column must have a defined dimension. "
                       "source_column: {}".format(source_column))

    if (not isinstance(boundaries, list) and
        not isinstance(boundaries, tuple)) or not boundaries:
      raise ValueError("boundaries must be a non-empty list or tuple. "
                       "boundaries: {}".format(boundaries))

    # We allow bucket boundaries to be monotonically increasing
    # (ie a[i+1] >= a[i]). When two bucket boundaries are the same, we
    # de-duplicate.
    sanitized_boundaries = []
    for i in range(len(boundaries) - 1):
      if boundaries[i] == boundaries[i + 1]:
        continue
      elif boundaries[i] < boundaries[i + 1]:
        sanitized_boundaries.append(boundaries[i])
      else:
        raise ValueError("boundaries must be a sorted list. "
                         "boundaries: {}".format(boundaries))
    sanitized_boundaries.append(boundaries[len(boundaries) - 1])

    return super(_BucketizedColumn, cls).__new__(cls, source_column,
                                                 tuple(sanitized_boundaries))

  @property
  def name(self):
    return "{}_bucketized".format(self.source_column.name)

  @property
  def length(self):
    """Returns total number of buckets."""
    return len(self.boundaries) + 1

  @property
  def config(self):
    return self.source_column.config

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return "{}".format(self)

  def insert_transformed_feature(self, columns_to_tensors):
    # Bucketize the source column.
    if self.source_column not in columns_to_tensors:
      self.source_column.insert_transformed_feature(columns_to_tensors)
    columns_to_tensors[self] = bucketization_op.bucketize(
        columns_to_tensors[self.source_column],
        boundaries=list(self.boundaries),
        name="bucketize")

  # pylint: disable=unused-argument
  def _to_dnn_input_layer(self,
                          input_tensor,
                          weight_collections=None,
                          trainable=True,
                          output_rank=2):
    if output_rank != 2:
      raise ValueError("BucketizedColumn currently only supports output_rank=2")
    return array_ops.reshape(
        array_ops.one_hot(
            math_ops.to_int64(input_tensor),
            self.length,
            1.,
            0.,
            name="one_hot"), [-1, self.length * self.source_column.dimension],
        name="reshape")

  def to_sparse_tensor(self, input_tensor):
    """Creates a SparseTensor from the bucketized Tensor."""
    dimension = self.source_column.dimension
    batch_size = array_ops.shape(input_tensor, name="shape")[0]

    if dimension > 1:
      i1 = array_ops.reshape(
          array_ops.tile(
              array_ops.expand_dims(
                  math_ops.range(0, batch_size), 1, name="expand_dims"),
              [1, dimension],
              name="tile"), [-1],
          name="reshape")
      i2 = array_ops.tile(
          math_ops.range(0, dimension), [batch_size], name="tile")
      # Flatten the bucket indices and unique them across dimensions
      # E.g. 2nd dimension indices will range from k to 2*k-1 with k buckets
      bucket_indices = array_ops.reshape(
          input_tensor, [-1], name="reshape") + self.length * i2
    else:
      # Simpler indices when dimension=1
      i1 = math_ops.range(0, batch_size)
      i2 = array_ops.zeros([batch_size], dtype=dtypes.int32, name="zeros")
      bucket_indices = array_ops.reshape(input_tensor, [-1], name="reshape")

    indices = math_ops.to_int64(array_ops.transpose(array_ops.stack((i1, i2))))
    shape = math_ops.to_int64(array_ops.stack([batch_size, dimension]))
    sparse_id_values = sparse_tensor_py.SparseTensor(
        indices, bucket_indices, shape)

    return sparse_id_values

  def _wide_embedding_lookup_arguments(self, input_tensor):
    return _LinearEmbeddingLookupArguments(
        input_tensor=self.to_sparse_tensor(input_tensor),
        weight_tensor=None,
        vocab_size=self.length * self.source_column.dimension,
        initializer=init_ops.zeros_initializer(),
        combiner="sum")


def bucketized_column(source_column, boundaries):
  """Creates a _BucketizedColumn for discretizing dense input.

  Args:
    source_column: A _RealValuedColumn defining dense column.
    boundaries: A list or tuple of floats specifying the boundaries. It has to
      be sorted.

  Returns:
    A _BucketizedColumn.

  Raises:
    ValueError: if 'boundaries' is empty or not sorted.
  """
  return _BucketizedColumn(source_column, boundaries)


class _CrossedColumn(_FeatureColumn,
                     collections.namedtuple("_CrossedColumn",
                                            ["columns", "hash_bucket_size",
                                             "hash_key",
                                             "combiner", "ckpt_to_load_from",
                                             "tensor_name_in_ckpt"])):
  """Represents a cross transformation also known as conjuction or combination.

  Instances of this class are immutable. It crosses given `columns`. Crossed
  column output will be hashed to hash_bucket_size.
  Conceptually, transformation can be thought as:
    Hash(cartesian product of features in columns) % `hash_bucket_size`

  For example, if the columns are

      SparseTensor referred by first column: shape = [2, 2]
      [0, 0]: "a"
      [1, 0]: "b"
      [1, 1]: "c"

      SparseTensor referred by second column: : shape = [2, 1]
      [0, 0]: "d"
      [1, 0]: "e"

  then crossed feature will look like:

      shape = [2, 2]
      [0, 0]: Hash64("d", Hash64("a")) % hash_bucket_size
      [1, 0]: Hash64("e", Hash64("b")) % hash_bucket_size
      [1, 1]: Hash64("e", Hash64("c")) % hash_bucket_size

  Attributes:
    columns: An iterable of _FeatureColumn. Items can be an instance of
      _SparseColumn, _CrossedColumn, or _BucketizedColumn.
    hash_bucket_size: An int that is > 1. The number of buckets.
    combiner: A string specifying how to reduce if there are multiple entries
      in a single row. Currently "mean", "sqrtn" and "sum" are supported, with
      "sum" the default. "sqrtn" often achieves good accuracy, in particular
      with bag-of-words columns. Each of this can be thought as example level
      normalizations on the column::
        * "sum": do not normalize
        * "mean": do l1 normalization
        * "sqrtn": do l2 normalization
      For more information: `tf.embedding_lookup_sparse`.
    ckpt_to_load_from: (Optional). String representing checkpoint name/pattern
      to restore the column weights. Required if `tensor_name_in_ckpt` is not
      None.
    tensor_name_in_ckpt: (Optional). Name of the `Tensor` in the provided
      checkpoint from which to restore the column weights. Required if
      `ckpt_to_load_from` is not None.

  Raises:
    TypeError: if all items in columns are not an instance of _SparseColumn,
      _CrossedColumn, or _BucketizedColumn.
    ValueError: if hash_bucket_size is not > 1 or len(columns) is not > 1. Also,
      if only one of `ckpt_to_load_from` and `tensor_name_in_ckpt` is specified.
  """

  @staticmethod
  def _assert_is_crossable(column):
    if isinstance(column, (_SparseColumn, _CrossedColumn, _BucketizedColumn)):
      return
    raise TypeError("columns must be a set of _SparseColumn, "
                    "_CrossedColumn, or _BucketizedColumn instances. "
                    "(column {} is a {})".format(column,
                                                 column.__class__.__name__))

  def __new__(cls,
              columns,
              hash_bucket_size,
              hash_key,
              combiner="sum",
              ckpt_to_load_from=None,
              tensor_name_in_ckpt=None):
    for column in columns:
      _CrossedColumn._assert_is_crossable(column)

    if len(columns) < 2:
      raise ValueError("columns must contain at least 2 elements. "
                       "columns: {}".format(columns))

    if hash_bucket_size < 2:
      raise ValueError("hash_bucket_size must be at least 2. "
                       "hash_bucket_size: {}".format(hash_bucket_size))

    if (ckpt_to_load_from is None) != (tensor_name_in_ckpt is None):
      raise ValueError("Must specify both `ckpt_to_load_from` and "
                       "`tensor_name_in_ckpt` or none of them.")

    sorted_columns = sorted(
        [column for column in columns], key=lambda column: column.name)
    return super(_CrossedColumn, cls).__new__(cls, tuple(sorted_columns),
                                              hash_bucket_size, hash_key,
                                              combiner,
                                              ckpt_to_load_from,
                                              tensor_name_in_ckpt)

  @property
  def name(self):
    sorted_names = sorted([column.name for column in self.columns])
    return "_X_".join(sorted_names)

  @property
  def config(self):
    config = {}
    for column in self.columns:
      config.update(_get_feature_config(column))
    return config

  @property
  def length(self):
    """Returns total number of buckets."""
    return self.hash_bucket_size

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return "{}".format(self)

  def id_tensor(self, input_tensor):
    """Returns the id tensor from the given transformed input_tensor."""
    return input_tensor

  # pylint: disable=unused-argument
  def weight_tensor(self, input_tensor):
    """Returns the weight tensor from the given transformed input_tensor."""
    return None

  def insert_transformed_feature(self, columns_to_tensors):
    """Handles cross transformation."""

    def _collect_leaf_level_columns(cross):
      """Collects base columns contained in the cross."""
      leaf_level_columns = []
      for c in cross.columns:
        if isinstance(c, _CrossedColumn):
          leaf_level_columns.extend(_collect_leaf_level_columns(c))
        else:
          leaf_level_columns.append(c)
      return leaf_level_columns

    feature_tensors = []
    for c in _collect_leaf_level_columns(self):
      if isinstance(c, _SparseColumn):
        feature_tensors.append(columns_to_tensors[c.name])
      else:
        if c not in columns_to_tensors:
          c.insert_transformed_feature(columns_to_tensors)
        if isinstance(c, _BucketizedColumn):
          feature_tensors.append(c.to_sparse_tensor(columns_to_tensors[c]))
        else:
          feature_tensors.append(columns_to_tensors[c])
    columns_to_tensors[self] = sparse_feature_cross_op.sparse_feature_cross(
        feature_tensors,
        hashed_output=True,
        num_buckets=self.hash_bucket_size,
        hash_key=self.hash_key,
        name="cross")

  # pylint: disable=unused-argument
  def _to_dnn_input_layer(self,
                          input_tensor,
                          weight_collections=None,
                          trainable=True,
                          output_rank=2):
    raise ValueError("CrossedColumn is not supported in DNN. "
                     "Please use embedding_column. column: {}".format(self))

  def _checkpoint_path(self):
    if self.ckpt_to_load_from is not None:
      return self.ckpt_to_load_from, self.tensor_name_in_ckpt
    return None

  def _wide_embedding_lookup_arguments(self, input_tensor):
    return _LinearEmbeddingLookupArguments(
        input_tensor=input_tensor,
        weight_tensor=None,
        vocab_size=self.length,
        initializer=init_ops.zeros_initializer(),
        combiner=self.combiner)


def crossed_column(columns, hash_bucket_size, combiner="sum",
                   ckpt_to_load_from=None,
                   tensor_name_in_ckpt=None,
                   hash_key=None):
  """Creates a _CrossedColumn for performing feature crosses.

  Args:
    columns: An iterable of _FeatureColumn. Items can be an instance of
      _SparseColumn, _CrossedColumn, or _BucketizedColumn.
    hash_bucket_size: An int that is > 1. The number of buckets.
    combiner: A string specifying how to reduce if there are multiple entries
      in a single row. Currently "mean", "sqrtn" and "sum" are supported, with
      "sum" the default. "sqrtn" often achieves good accuracy, in particular
      with bag-of-words columns. Each of this can be thought as example level
      normalizations on the column::
        * "sum": do not normalize
        * "mean": do l1 normalization
        * "sqrtn": do l2 normalization
      For more information: `tf.embedding_lookup_sparse`.
    ckpt_to_load_from: (Optional). String representing checkpoint name/pattern
      to restore the column weights. Required if `tensor_name_in_ckpt` is not
      None.
    tensor_name_in_ckpt: (Optional). Name of the `Tensor` in the provided
      checkpoint from which to restore the column weights. Required if
      `ckpt_to_load_from` is not None.
    hash_key: Specify the hash_key that will be used by the `FingerprintCat64`
      function to combine the crosses fingerprints on SparseFeatureCrossOp
      (optional).

  Returns:
    A _CrossedColumn.

  Raises:
    TypeError: if any item in columns is not an instance of _SparseColumn,
      _CrossedColumn, or _BucketizedColumn, or
      hash_bucket_size is not an int.
    ValueError: if hash_bucket_size is not > 1 or
      len(columns) is not > 1.
  """
  return _CrossedColumn(
      columns,
      hash_bucket_size,
      hash_key,
      combiner=combiner,
      ckpt_to_load_from=ckpt_to_load_from,
      tensor_name_in_ckpt=tensor_name_in_ckpt)


class DataFrameColumn(_FeatureColumn,
                      collections.namedtuple("DataFrameColumn",
                                             ["column_name", "series"])):
  """Represents a feature column produced from a `DataFrame`.

  Instances of this class are immutable.  A `DataFrame` column may be dense or
  sparse, and may have any shape, with the constraint that dimension 0 is
  batch_size.

  Args:
    column_name: a name for this column
    series: a `Series` to be wrapped, which has already had its base features
      substituted with `PredefinedSeries`.
  """

  def __new__(cls, column_name, series):
    return super(DataFrameColumn, cls).__new__(cls, column_name, series)

  @property
  def name(self):
    return self.column_name

  @property
  def config(self):
    return self.series.required_base_features()

  @property
  def key(self):
    """Returns a string which will be used as a key when we do sorting."""
    return self.name

  def insert_transformed_feature(self, columns_to_tensors):
    # The cache must already contain mappings from the expected base feature
    # names to Tensors.

    # Passing columns_to_tensors as the cache here means that multiple outputs
    # of the transform will be cached, keyed by the repr of their associated
    # TransformedSeries.
    # The specific requested output ends up in columns_to_tensors twice: once
    # keyed by the TransformedSeries repr, and once keyed by this
    # DataFrameColumn instance.
    columns_to_tensors[self] = self.series.build(columns_to_tensors)

  # pylint: disable=unused-argument
  def _to_dnn_input_layer(self,
                          input_tensor,
                          weight_collections=None,
                          trainable=True,
                          output_rank=2):
    if input_tensor.dtype != dtypes.float32:
      input_tensor = math_ops.to_float(input_tensor)
    return _reshape_real_valued_tensor(input_tensor, output_rank, self.name)

  def _to_dense_tensor(self, input_tensor):
    return self._to_dnn_input_layer(input_tensor)

  def __eq__(self, other):
    if isinstance(other, self.__class__):
      return self.__dict__ == other.__dict__
    else:
      return False

  def __ne__(self, other):
    return not self.__eq__(other)


def _get_feature_config(feature_column):
  """Returns configuration for the base feature defined in feature_column."""
  if not isinstance(feature_column, _FeatureColumn):
    raise TypeError(
        "feature_columns should only contain instances of _FeatureColumn. "
        "Given column is {}".format(feature_column))
  if isinstance(feature_column, (_SparseColumn, _WeightedSparseColumn,
                                 _EmbeddingColumn, _RealValuedColumn,
                                 _BucketizedColumn, _CrossedColumn,
                                 _OneHotColumn, _ScatteredEmbeddingColumn)):
    return feature_column.config

  raise TypeError("Not supported _FeatureColumn type. "
                  "Given column is {}".format(feature_column))


def create_feature_spec_for_parsing(feature_columns):
  """Helper that prepares features config from input feature_columns.

  The returned feature config can be used as arg 'features' in tf.parse_example.

  Typical usage example:

  ```python
  # Define features and transformations
  feature_a = sparse_column_with_vocabulary_file(...)
  feature_b = real_valued_column(...)
  feature_c_bucketized = bucketized_column(real_valued_column("feature_c"), ...)
  feature_a_x_feature_c = crossed_column(
    columns=[feature_a, feature_c_bucketized], ...)

  feature_columns = set(
    [feature_b, feature_c_bucketized, feature_a_x_feature_c])
  batch_examples = tf.parse_example(
      serialized=serialized_examples,
      features=create_feature_spec_for_parsing(feature_columns))
  ```

  For the above example, create_feature_spec_for_parsing would return the dict:
  {
    "feature_a": parsing_ops.VarLenFeature(tf.string),
    "feature_b": parsing_ops.FixedLenFeature([1], dtype=tf.float32),
    "feature_c": parsing_ops.FixedLenFeature([1], dtype=tf.float32)
  }

  Args:
    feature_columns: An iterable containing all the feature columns. All items
      should be instances of classes derived from _FeatureColumn, unless
      feature_columns is a dict -- in which case, this should be true of all
      values in the dict.
  Returns:
    A dict mapping feature keys to FixedLenFeature or VarLenFeature values.
  """
  if isinstance(feature_columns, dict):
    feature_columns = feature_columns.values()

  features_config = {}
  for column in feature_columns:
    features_config.update(_get_feature_config(column))
  return features_config


def _create_sequence_feature_spec_for_parsing(sequence_feature_columns,
                                              allow_missing_by_default=False):
  """Prepares a feature spec for parsing `tf.SequenceExample`s.

  Args:
    sequence_feature_columns: an iterable containing all the feature columns.
      All items should be instances of classes derived from `_FeatureColumn`.
    allow_missing_by_default: whether to set `allow_missing=True` by default for
      `FixedLenSequenceFeature`s.
  Returns:
    A dict mapping feature keys to `FixedLenSequenceFeature` or `VarLenFeature`.
  """
  feature_spec = create_feature_spec_for_parsing(sequence_feature_columns)
  sequence_feature_spec = {}
  for key, feature in feature_spec.items():
    if isinstance(feature, parsing_ops.VarLenFeature):
      sequence_feature = feature
    elif isinstance(feature, parsing_ops.FixedLenFeature):
      default_is_set = feature.default_value is not None
      if default_is_set:
        logging.warning(
            'Found default value {} for feature "{}". Ignoring this value and '
            'setting `allow_missing=True` instead.'.
            format(feature.default_value, key))
      sequence_feature = parsing_ops.FixedLenSequenceFeature(
          shape=feature.shape,
          dtype=feature.dtype,
          allow_missing=(allow_missing_by_default or default_is_set))
    else:
      raise TypeError(
          "Unsupported feature type: {}".format(type(feature).__name__))
    sequence_feature_spec[key] = sequence_feature
  return sequence_feature_spec


def make_place_holder_tensors_for_base_features(feature_columns):
  """Returns placeholder tensors for inference.

  Args:
    feature_columns: An iterable containing all the feature columns. All items
      should be instances of classes derived from _FeatureColumn.
  Returns:
    A dict mapping feature keys to SparseTensors (sparse columns) or
    placeholder Tensors (dense columns).
  """
  # Get dict mapping features to FixedLenFeature or VarLenFeature values.
  dict_for_parse_example = create_feature_spec_for_parsing(feature_columns)
  placeholders = {}
  for column_name, column_type in dict_for_parse_example.items():
    if isinstance(column_type, parsing_ops.VarLenFeature):
      # Sparse placeholder for sparse tensors.
      placeholders[column_name] = array_ops.sparse_placeholder(
          column_type.dtype, name="Placeholder_{}".format(column_name))
    else:
      # Simple placeholder for dense tensors.
      placeholders[column_name] = array_ops.placeholder(
          column_type.dtype,
          shape=(None, column_type.shape[0]),
          name="Placeholder_{}".format(column_name))
  return placeholders


class _SparseIdLookupConfig(
    collections.namedtuple("_SparseIdLookupConfig",
                           ["vocabulary_file", "keys", "num_oov_buckets",
                            "vocab_size", "default_value"])):
  """Defines lookup configuration for a sparse feature.

  An immutable object defines lookup table configuration used by
  tf.feature_to_id_v2.

  Attributes:
    vocabulary_file: The vocabulary filename. vocabulary_file cannot be combined
      with keys.
    keys: A 1-D string iterable that specifies the mapping of strings to
      indices. It means a feature in keys will map to it's index in keys.
    num_oov_buckets: The number of out-of-vocabulary buckets. If zero all out of
      vocabulary features will be ignored.
    vocab_size: Number of the elements in the vocabulary.
    default_value: The value to use for out-of-vocabulary feature values.
      Defaults to -1.
  """

  def __new__(cls,
              vocabulary_file=None,
              keys=None,
              num_oov_buckets=0,
              vocab_size=None,
              default_value=-1):

    return super(_SparseIdLookupConfig, cls).__new__(cls, vocabulary_file, keys,
                                                     num_oov_buckets,
                                                     vocab_size, default_value)
