(self)
The node immediately preceding the invocant in their parent's children
        list. If the invocant does not have a previous sibling, it is None.
The node immediately preceding the invocant in their parent's children
        list. If the invocant does not have a previous sibling, it is None.
The node immediately preceding the invocant in their parent s children list . If the invocant does not have a previous sibling it is None .
def prev_sibling(self):
        """
        The node immediately preceding the invocant in their parent's children
        list. If the invocant does not have a previous sibling, it is None.
        """
        if self.parent is None:
            return None

        # Can't use index(); we need to test by identity
        for i, child in enumerate(self.parent.children):
            if child is self:
                if i == 0:
                    return None
                return self.parent.children[i-1]
def prev_sibling ( self ) : if self . parent is None : return None # Can't use index(); we need to test by identity for i , child in enumerate ( self . parent . children ) : if child is self : if i == 0 : return None return self . parent . children [ i - 1 ]