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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 call_purge_doc(cls, kb_app, sphinx_app: Sphinx, sphinx_env: BuildEnvironment, docname: str):
 """ On env-purge-doc, do callbacks """


        for callback in EventAction.get_callbacks(kb_app, SphinxEvent.EPD):
            callback(kb_app, sphinx_app, sphinx_env, docname)