import json


def read_body_part_weights(body_part_json):
  """
  Reads from a JSON formatted file the set of body parts and their
  weights.

  Args:
      body_part_json (json): a JSON formatted specifying body parts
                      and weights

  Returns:
      list: list of weights indexed by body parts
  """
  with open(body_part_json) as data_file:
    weights = json.load(data_file)['weights']
    return weights