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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 num_pending(self, work_spec_name):
        '''Get the number of pending work units for some work spec.

        These are work units that some worker is currently working on
        (hopefully; it could include work units assigned to workers that
        died and that have not yet expired).

        '''
        return self.registry.len(WORK_UNITS_ + work_spec_name,
                                 priority_min=time.time())