title: Python - JSON to CSV converter explanation
body: <p>I am doing a data analysis project and I need to convert the files from JSON to CSV. I have discovered this code but as I have not studied Python yet I'm unsure what to do. I'm not sure where I put the file directory or the column names.</p>
  
  <p>If someone would be able to explain where I do this I'd appreciate it!</p>
  
  <pre><code>import argparse
  import collections
  import csv
  import simplejson 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)
  </code></pre>