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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 wait_for_providers(self):
 """ Wait for any providers registered with the collector to have unregistered. Returns immediately if no providers were ever registered. """

        if self._providers_registered:
            _log.debug('waiting for providers to unregister %s', self)
            self._last_provider_unregistered.wait()
            _log.debug('all providers unregistered %s', self)