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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 post_processor_affected_function( exposure=None, hazard=None, classification=None, hazard_class=None):
 """Private function used in the affected postprocessor. It returns a boolean if it's affected or not, or not exposed. :param exposure: The exposure to use. :type exposure: str :param hazard: The hazard to use. :type hazard: str :param classification: The hazard classification to use. :type classification: str :param hazard_class: The hazard class of the feature. :type hazard_class: str :return: If this hazard class is affected or not. It can be `not exposed`. The not exposed value returned is the key defined in `hazard_classification.py` at the top of the file. :rtype: bool,'not exposed' """

    if exposure == exposure_population['key']:
        affected = is_affected(
            hazard, classification, hazard_class)
    else:
        classes = None
        for hazard in hazard_classes_all:
            if hazard['key'] == classification:
                classes = hazard['classes']
                break

        for the_class in classes:
            if the_class['key'] == hazard_class:
                affected = the_class['affected']
                break
        else:
            affected = not_exposed_class['key']

    return affected