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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 to_cache_timer(datetime_func):
 """Converts a datetime_func to a timestamp_func. Args: datetime_func (callable[[datatime]]):
 a func that returns the current time Returns: time_func (callable[[timestamp]):
 a func that returns the timestamp from the epoch """

    if datetime_func is None:
        datetime_func = datetime.utcnow

    def _timer():
        """Return the timestamp since the epoch."""
        return (datetime_func() - datetime(1970, 1, 1)).total_seconds()

    return _timer