shadowed variables not noticed after list comprehension

[Brian Warner]

With pyflakes-0.8.1 and python-2.7.8, the following test program gets the expected complaint:

import foo
foo()
def bar():
    a = 0
    #a = [1 for foo in []]
    for foo in []:
        pass
    del a

pyflakes t.py
t.py:6: import 'foo' from line 1 shadowed by loop variable

But if you uncomment the list comprehension, the pyflakes complaints go away.

I think the presence of the list comprehension should actually *increase* the number of complaints: "foo" is being shadowed in both the list comprehension and the for-loop.

[Ian Cordasco (icordasc)]

You mention this happens on 2.7. The 2.x branch has an issue with list comprehension bindings being leaked to the outer scope. So you can do this on 2.7

[i for i in range(10)]
print(i + 1)

And you'll see 10.

I agree that uncommenting the list comprehension shouldn't cause the error to stop but I suspect what I mentioned is what's causing it. It appears, to pyflakes, that the variable is being defined locally in some way that does not appear to shadow the global binding.

I think I agree that there should also be (ideally) two errors/warnings: 1 for using `foo` in the list comprehension and 1 for using it afterwards.