Getting parent of AST node in Python

Here's some actual code:

for node in ast.walk(root):
    for child in ast.iter_child_nodes(node):
        child.parent = node

There's no need for a hash table, you can just put an attribute directly on the node.

You can also use ast.NodeTransformer to achieve this:

Code:

import ast


class Parentage(ast.NodeTransformer):
    # current parent (module)
    parent = None

    def visit(self, node):
        # set parent attribute for this node
        node.parent = self.parent
        # This node becomes the new parent
        self.parent = node
        # Do any work required by super class 
        node = super().visit(node)
        # If we have a valid node (ie. node not being removed)
        if isinstance(node, ast.AST):
            # update the parent, since this may have been transformed 
            # to a different node by super
            self.parent = node.parent
        return node

Usage:

module = Parentage().visit(ast.parse('def _(): ...'))
assert module.parent is None
assert module.body[0].parent is module

Later on when you want to edit the tree in some other way, you can subclass:

class SomeRefactoring(Parentage):
    def visit_XXX(node):
        self.generic_visit(node)
        f'do some work on {node.parent} here if you want'
        return node

Note:

Its worth noting that some nodes can have multiple parents. For example:

module = ast.parse("warnings.warn('Dinosaurs!')")
func = module.body[0].value.func
name, ctx = ast.iter_child_nodes(func)
assert ctx is next(ast.iter_child_nodes(name))

Which shows that the same ast.Load node ctx has two parents - func and name. The parent will be set by the last position that the node appears in in the tree.

It wouldn't be really be a plugin, but you can always write a function which adds a weakref to parent in every child.