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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 timesince_or_never(dt, default=None):
 """Call the Django ``timesince`` filter or a given default string. It returns the string *default* if *dt* is not a valid ``date`` or ``datetime`` object. When *default* is None, "Never" is returned. """

    if default is None:
        default = _("Never")

    if isinstance(dt, datetime.date):
        return timesince(dt)
    else:
        return default