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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 split(self, pat, side='left'):
 """Split once each element from the left and select a side to return. Note this is unlike pandas split in that it essentially combines the split with a select. Parameters pat : str side : {'left', 'right'} Which side of the split to select and return in each element. Returns ------- Series """

        check_type(pat, str)
        check_type(side, str)

        # don't want this made with the object
        _split_mapping = {
            'left': 0,
            'right': 1
        }

        if side not in _split_mapping:
            raise ValueError('Can only select left or right side of split')

        return _series_str_result(self, weld_str_split, pat=pat, side=_split_mapping[side])