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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 check_time(value):
 """Convert time from most popular representations to datetime"""

    if value is None:
        return None
    if isinstance(value, (time.struct_time, tuple)):
        return value
    if isinstance(value, datetime.datetime):
        return value.timetuple()
    if isinstance(value, datetime.date):
        res = datetime.datetime.utcnow()
        res.replace(year=value.year, month=value.month, day=value.day)
        return res.timetuple()
    if isinstance(value, datetime.time):
        return datetime.datetime.combine(datetime.date.today(),
                                         value).timetuple()
    if isinteger(value):
        # Handle integer as timestamp
        return time.gmtime(value)
    if isinstance(value, basestring):
        if value.lower() == 'now':
            return time.gmtime()
        # TODO: parsinng some popular strings
    raise ValueError("Unsupported time representation:" + repr(value))