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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 _getArgNames(spec):
 """ Get the name of all arguments defined in a function signature. The name of * and ** arguments is normalized to "*args" and "**kwargs". :param ArgSpec spec: A function to interrogate for a signature. :return: The set of all argument names in `func`s signature. :rtype: Set[str] """

    return set(
        spec.args
        + spec.kwonlyargs
        + (('*args',) if spec.varargs else ())
        + (('**kwargs',) if spec.varkw else ())
        + spec.annotations
    )