Python: deeply copy ast node tree

Question

I'm trying to use deepcopy (from the copy module) to deeply copy a node tree from the ast module.

This doesn't seem to work. I'm getting strange errors like TypeError: required field "name" missing from FunctionDef when I use the copied result (and I checked it; it really is missing in the copied node), so it didn't correctly copied them.

Is there a trick I can make this working? Or maybe am I missing something?

Answer 1

Sorry, I was wrong. copy.deepcopy seems to work correct. The reason I thought it wouldn't work is because of this very odd behavior:

import ast, copy
n = ast.FunctionDef(
        name=None,
        args=ast.arguments(args=[], vararg=None, kwarg=None, defaults=[]),
        body=[], decorator_list=[])
n.name = "foo"
ast.fix_missing_locations(n)
n = copy.deepcopy(n)
print n.name

This returns None in PyPy. Probably a bug because in CPython 2.6, I get foo. Strangely, in PyPy, if I remove name=None from the ast.FunctionDef call, I also get foo as the output.

I created a bug report for PyPy about this.