def GetGtfsClassByFileName(self, filename):
    if filename not in self._file_mapping:
      return None
    mapping = self._file_mapping[filename]
    class_list = mapping['classes']
    if len(class_list) > 1:
      raise problems.NonStandardMapping(filename)
    else:
      return self._class_mapping[class_list[0]]
Handle the implicit VS .idl rule for one source file. Fills |outputs|
dataset/ETHPy150Open google/transitfeed/transitfeed/gtfsfactory.py/GtfsFactory.GetGtfsClassByFileName--crossover with--dataset/ETHPy150Open adobe/brackets-shell/gyp/pylib/gyp/generator/ninja.py/NinjaWriter._WinIdlRule