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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 _get_exception_class_from_status_code(status_code):
 """ Utility function that accepts a status code, and spits out a reference to the correct exception class to raise. :param str status_code: The status code to return an exception class for. :rtype: PetfinderAPIError or None :returns: The appropriate PetfinderAPIError subclass. If the status code is not an error, return ``None``. """

    if status_code == '100':
        return None

    exc_class = STATUS_CODE_MAPPING.get(status_code)
    if not exc_class:
        # No status code match, return the "I don't know wtf this is"
        # exception class.
        return STATUS_CODE_MAPPING['UNKNOWN']
    else:
        # Match found, yay.
        return exc_class