code: def resolve_freezer(freezer):
      
      # Set default freezer if there was none
      if not freezer:
          return _Default()
  
      # Allow character based lookups as well
      if isinstance(freezer, six.string_types):
          cls = _freezer_lookup(freezer)
          return cls()
  
      # Allow plain class definition lookups (we instantiate the class)
      if freezer.__class__ == type.__class__:
          return freezer()
  
      # Warn when a custom freezer implementation is used.
      if freezer not in FREEZER.ALL:
          warn(u"Using custom freezer implelmentation: {0}".format(freezer))
  
      return freezer
docs: Locate the appropriate freezer given FREEZER or string input from the programmer.
  
      :param freezer: FREEZER constant or string for the freezer that is requested.  (None = FREEZER.DEFAULT)
      :return: