code: def AppendFlagsIntoFile(self, filename):
      
      with open(filename, 'a') as out_file:
        out_file.write(self.FlagsIntoString())
docs: Appends all flags assignments from this FlagInfo object to a file.
  
      Output will be in the format of a flagfile.
  
      NOTE: MUST mirror the behavior of the C++ AppendFlagsIntoFile
      from http://code.google.com/p/google-gflags
  
      Args:
        filename: string, name of the file.