old_contents: import datetime
  
  from twilio import values
  
  
  def iso8601_date(d):
      """
      Return a string representation of a date that the Twilio API understands
      Format is YYYY-MM-DD. Returns None if d is not a string, datetime, or date
      """
      if d == values.unset:
          return d
      elif isinstance(d, datetime.datetime):
          return str(d.date())
      elif isinstance(d, datetime.date):
          return str(d)
      elif isinstance(d, str):
          return d
  
  
  def iso8601_datetime(d):
      """
      Return a string representation of a date that the Twilio API understands
      Format is YYYY-MM-DD. Returns None if d is not a string, datetime, or date
      """
      if d == values.unset:
          return d
      elif isinstance(d, datetime.datetime) or isinstance(d, datetime.date):
          return d.strftime('%Y-%m-%dT%H:%M:%SZ')
      elif isinstance(d, str):
          return d
  
  
  def prefixed_collapsible_map(m, prefix):
      """
      Return a dict of params corresponding to those in m with the added prefix
      """
      if m == values.unset:
          return {}
  
      def flatten_dict(d, result={}, prv_keys=[]):
          for k, v in d.iteritems():
              if isinstance(v, dict):
                  flatten_dict(v, result, prv_keys + [k])
              else:
                  result['.'.join(prv_keys + [k])] = v
  
          return result
  
      if isinstance(m, dict):
          flattened = flatten_dict(m)
          return {'{}.{}'.format(prefix, k): v for k, v in flattened.items()}
  
      return {}
  
new_contents: import datetime
  
  from twilio import values
  
  
  def iso8601_date(d):
      """
      Return a string representation of a date that the Twilio API understands
      Format is YYYY-MM-DD. Returns None if d is not a string, datetime, or date
      """
      if d == values.unset:
          return d
      elif isinstance(d, datetime.datetime):
          return str(d.date())
      elif isinstance(d, datetime.date):
          return str(d)
      elif isinstance(d, str):
          return d
  
  
  def iso8601_datetime(d):
      """
      Return a string representation of a date that the Twilio API understands
      Format is YYYY-MM-DD. Returns None if d is not a string, datetime, or date
      """
      if d == values.unset:
          return d
      elif isinstance(d, datetime.datetime) or isinstance(d, datetime.date):
          return d.strftime('%Y-%m-%dT%H:%M:%SZ')
      elif isinstance(d, str):
          return d
  
  
  def prefixed_collapsible_map(m, prefix):
      """
      Return a dict of params corresponding to those in m with the added prefix
      """
      if m == values.unset:
          return {}
  
      def flatten_dict(d, result={}, prv_keys=[]):
          for k, v in d.items():
              if isinstance(v, dict):
                  flatten_dict(v, result, prv_keys + [k])
              else:
                  result['.'.join(prv_keys + [k])] = v
  
          return result
  
      if isinstance(m, dict):
          flattened = flatten_dict(m)
          return {'{}.{}'.format(prefix, k): v for k, v in flattened.items()}
  
      return {}
  
subject: Use .items instead of .iteritems