def add_defaults(self, defaults):
        """Add defaults to this object, overwriting any which already exist"""
        # Since we can't check for immutability reliably, shallow copy the
        # value. If a mutable value were set and it were changed in one place
        # it would affect all other instances, since this is typically called
        # on __init__
        self._variable_defaults.update((d[0], copy.copy(d[1])) for d in defaults)
Add defaults to this object, overwriting any which already exist
libqtile/configurable.py