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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 fixed_timezone(offset):
 # type: (int) -> _FixedTimezone """ Return a Timezone instance given its offset in seconds. """

    if offset in _tz_cache:
        return _tz_cache[offset]

    tz = _FixedTimezone(offset)
    _tz_cache[offset] = tz

    return tz