code: def FlagsIntoString(self):
      
      s = ''
      for flag in self.FlagDict().values():
        if flag.value is not None:
          s += flag.serialize() + '\n'
      return s
docs: Returns a string with the flags assignments from this FlagValues object.
  
      This function ignores flags whose value is None.  Each flag
      assignment is separated by a newline.
  
      NOTE: MUST mirror the behavior of the C++ CommandlineFlagsIntoString
      from http://code.google.com/p/google-gflags
  
      Returns:
        string with the flags assignments from this FlagValues object.