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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 current_guard():
 """ Fetches the current instance of flask-praetorian that is attached to the current flask app """

    guard = flask.current_app.extensions.get('praetorian', None)
    PraetorianError.require_condition(
        guard is not None,
        "No current guard found; Praetorian must be initialized first",
    )
    return guard