Method add

lib/sqlalchemy/sql/base.py:2040–2068

(  # type: ignore[override]
        self, column: _NAMEDCOL, key: Optional[str] = None
    )

    """

    def add(  # type: ignore[override]
        self, column: _NAMEDCOL, key: Optional[str] = None
    ) -> None:
        if key is not None and column.key != key:
            raise exc.ArgumentError(
                "DedupeColumnCollection requires columns be under "
                "the same key as their .key"
            )
        key = column.key

        if key is None:
            raise exc.ArgumentError(
                "Can't add unnamed column to column collection"
            )

        if key in self._index:
            existing = self._index[key][1]

            if existing is column:
                return

            self.replace(column)

            # pop out memoized proxy_set as this
            # operation may very well be occurring
            # in a _make_proxy operation
            util.memoized_property.reset(column, "proxy_set")
        else:
            self._append_new_column(key, column)

    def _append_new_column(self, key: str, named_column: _NAMEDCOL) -> None:
        l = len(self._collection)