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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 _convert(value, tzto, defaulttz):
 """Convert datetime.datetime object between timezones"""

    if not isinstance(value, datetime):
        raise ValueError('value must be a datetime.datetime object')

    if value.tzinfo is None:
        value = value.replace(tzinfo=defaulttz)

    return value.astimezone(tzto)