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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 datetime_from_json(js, manager):
 """Deserialize a Python datetime object from json."""

    if js is None:
        return None
    else:
        return dt.datetime(
            js['year'],
            js['month'] + 1,  # Months are 1-based in Python
            js['date'],
            js['hours'],
            js['minutes'],
            js['seconds'],
            js['milliseconds'] * 1000
        )