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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 _grid_col(self):
 """ The grid column at which this cell begins. """

        tr = self._tr
        idx = tr.tc_lst.index(self)
        preceding_tcs = tr.tc_lst[:idx]
        return sum(tc.grid_span for tc in preceding_tcs)