exec doesn't pick up variables from closure

问题:

I'm a little curious why the following code raises a NameError.

>>> s = """
... foo = [1,2,3]
... def bar():
...    return foo[1]
... """
>>> namespace = {}
>>> exec(s, {'__builtins__': None}, namespace)
>>> print namespace
{'foo': [1, 2, 3], 'bar': <function bar at 0x7f79871bd0c8>}
>>> namespace['bar']()

At the normal interpreter level, we can find foo in bar.func_globals or bar.func_closure if in a function. I guess I'm wondering why namespace['bar'] doesn't put foo in func_closure ...

回答1:

It turns out that the answer was there all along in the docs:

If two separate objects are given as globals and locals, the code will be executed as if it were embedded in a class definition.

Since I'm passing in both globals and locals, it executes as if it were in a class.

class Foo(object):
    foo = [1,2,3]
    @staticmethod
    def bar():
       return foo[1]

not surprisingly doesn't work either :).

For anyone interested in a workaround, you can inject namespace back into namespace['bar'].func_globals¹ (inspired by this):

>>> namespace['bar'].func_globals.update(namespace)
>>> namespace['bar']()
2

Nice.

^{1It would be namespace['bar'].__globals__.update on python3.x}