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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def EmitProto(cls):
 """Emits .proto file definitions."""

    result = "message %s {\n" % cls.__name__
    for _, desc in sorted(iteritems(cls.type_infos_by_field_number)):
      result += desc.Definition()

    result += "}\n"
    return result