import six


def as_bytes(bytes_or_text, encoding='utf-8'):
    """Converts bytes or unicode to `bytes`, using utf-8 encoding for text.

    # Arguments
        bytes_or_text: A `bytes`, `str`, or `unicode` object.
        encoding: A string indicating the charset for encoding unicode.

    # Returns
        A `bytes` object.

    # Raises
        TypeError: If `bytes_or_text` is not a binary or unicode string.
    """
    if isinstance(bytes_or_text, six.text_type):
        return bytes_or_text.encode(encoding)
    elif isinstance(bytes_or_text, bytes):
        return bytes_or_text
    else:
        raise TypeError('Expected binary or unicode string, got %r' %
                        (bytes_or_text,))