def _select(self, name: str, sel: str | int | None) -> CommandObject | None:
        """Select the given item of the given item class

        This method is called with the following guarantees:
            - `name` is a valid selector class for this item
            - `sel` is a valid selector for this item
            - the `(name, sel)` tuple is not an "impossible" combination (e.g. a
              selector is specified when `name` is not a containment object).

        Return None if no such object exists
        """
Select the given item of the given item class

        This method is called with the following guarantees:
            - `name` is a valid selector class for this item
            - `sel` is a valid selector for this item
            - the `(name, sel)` tuple is not an "impossible" combination (e.g. a
              selector is specified when `name` is not a containment object).

        Return None if no such object exists
        
libqtile/command/base.py