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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 birthday(self):
 """ Return a string representing the age of the process. """

        if isfile(self.pid_file):
            
            # Timestamp / timezone string
            tstamp  = datetime.fromtimestamp(self.created())
            tzone   = tzname[0] 
            weekday = WEEKDAY[tstamp.isoweekday()]
            
            # PID file age / age string
            age     = self.age()
            age_str = '{}s ago'.format(age[0]) 
            
            # Birthday string
            bday   = '{} {} {}; {}'.format(weekday, tstamp, tzone, age_str)
            
            # Return timestamp / timestamp string
            return (self.created(), bday)
        return (None, None)