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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 _set_item(self, key, value):
 """ Add series to DataFrame in specified column. If series is a numpy-array (not a Series/TimeSeries), it must be the same length as the DataFrames index or an error will be thrown. Series/TimeSeries will be conformed to the DataFrames index to ensure homogeneity. """


        self._ensure_valid_index(value)
        value = self._sanitize_column(key, value)
        NDFrame._set_item(self, key, value)

        # check if we are modifying a copy
        # try to set first as we want an invalid
        # value exception to occur first
        if len(self):
            self._check_setitem_copy()