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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 initialize(signal_number=DEFAULT_TIMER_SIGNAL_NUMBER, update_period_s=DEFAULT_UPDATE_PERIOD_S):
 """Initialize metrics, must be invoked at least once prior to invoking any other method."""

    global initialized
    if initialized:
        return
    initialized = True
    uwsgi.add_timer(signal_number, update_period_s)
    uwsgi.register_signal(signal_number, MULE, emit)