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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 groupby(expr, by, *bys):
 """ Group collection by a series of sequences. :param expr: collection :param by: columns to group :param bys: columns to group :return: GroupBy instance :rtype: :class:`odps.df.expr.groupby.GroupBy` """


    if not isinstance(by, list):
        by = [by, ]
    if len(bys) > 0:
        by = by + list(bys)
    return GroupBy(_input=expr, _by=by)