text: # -*- coding: utf-8 -*-
  """Convert the Yelp Dataset Challenge dataset from json format to csv.
  
  For more information on the Yelp Dataset Challenge please visit http://yelp.com/dataset_challenge
  
  """
  import argparse
  import collections
  import csv
  import ujson as json
  
  
  def read_and_write_file(json_file_path, csv_file_path, column_names):
      """Read in the json dataset file and write it out to a csv file, given the column names."""
      with open(csv_file_path, 'wb+') as fout:
          csv_file = csv.writer(fout)
          csv_file.writerow(list(column_names))
          with open(json_file_path) as fin:
              for line in fin:
                  line_contents = json.loads(line)
                  csv_file.writerow(get_row(line_contents, column_names))
  
  def get_superset_of_column_names_from_file(json_file_path):
      """Read in the json dataset file and return the superset of column names."""
      column_names = set()
      with open(json_file_path) as fin:
          for line in fin:
              line_contents = json.loads(line)
              column_names.update(
                      set(get_column_names(line_contents).keys())
                      )
      return column_names
  
  def get_column_names(line_contents, parent_key=''):
      """Return a list of flattened key names given a dict.
  
      Example:
  
          line_contents = {
              'a': {
                  'b': 2,
                  'c': 3,
                  },
          }
  
          will return: ['a.b', 'a.c']
  
      These will be the column names for the eventual csv file.
  
      """
      column_names = []
      for k, v in line_contents.iteritems():
          column_name = "{0}.{1}".format(parent_key, k) if parent_key else k
          if isinstance(v, collections.MutableMapping):
              column_names.extend(
                      get_column_names(v, column_name).items()
                      )
          else:
              column_names.append((column_name, v))
      return dict(column_names)
  
  def get_nested_value(d, key):
      """Return a dictionary item given a dictionary `d` and a flattened key from `get_column_names`.
      
      Example:
  
          d = {
              'a': {
                  'b': 2,
                  'c': 3,
                  },
          }
          key = 'a.b'
  
          will return: 2
      
      """
      if '.' not in key:
          if key not in d:
              return None
          return d[key]
      base_key, sub_key = key.split('.', 1)
      if base_key not in d:
          return None
      sub_dict = d[base_key]
      return get_nested_value(sub_dict, sub_key)
  
  def get_row(line_contents, column_names):
      """Return a csv compatible row given column names and a dict."""
      row = []
      for column_name in column_names:
          line_value = get_nested_value(
                          line_contents,
                          column_name,
                          )
          if isinstance(line_value, unicode):
              row.append('{0}'.format(line_value.encode('utf-8')))
          elif line_value is not None:
              row.append('{0}'.format(line_value))
          else:
              row.append('')
      return row
  
  if __name__ == '__main__':
      """Convert a yelp dataset file from json to csv."""
  
      parser = argparse.ArgumentParser(
              description='Convert Yelp Dataset Challenge data from JSON format to CSV.',
              )
  
      parser.add_argument(
              'json_file',
              type=str,
              help='The json file to convert.',
              )
  
      args = parser.parse_args()
  
      json_file = args.json_file
      csv_file = '{0}.csv'.format(json_file.split('.json')[0])
  
      column_names = get_superset_of_column_names_from_file(json_file)
      read_and_write_file(json_file, csv_file, column_names)
  