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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 to_utc(a_datetime, keep_utc_tzinfo=False):
 """ Convert a time awared datetime to utc datetime. :param a_datetime: a timezone awared datetime. (If not, then just returns) :param keep_utc_tzinfo: whether to retain the utc time zone information. **中文文档** 将一个带时区的时间转化成UTC时间。而对于UTC时间而言, 有没有时区信息都无所谓了。 """

    if a_datetime.tzinfo:
        utc_datetime = a_datetime.astimezone(utc)  # convert to utc time
        if keep_utc_tzinfo is False:
            utc_datetime = utc_datetime.replace(tzinfo=None)
        return utc_datetime
    else:
        return a_datetime