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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 load_joke(service_num=1):
 """Pulls the joke from the service based on the argument. It is expected that all services used will return a string when successful or None otherwise. """

    result = {
      1 : ronswanson.get_joke(),
      2 : chucknorris.get_joke(),
      3 : catfacts.get_joke(),
      4 : dadjokes.get_joke(),
    }.get(service_num)

    return result