False positive with E1136 unsubscriptable-object

[sam-s]

Steps to reproduce

1. Create file z.py

a = None
while True:
    if a is None or a["1"] == 0:
        a = {"1":1}
    else:
        break
print "Done"

2. run pylint z.py

Current behavior

E:  3,20: Value 'a' is unsubscriptable (unsubscriptable-object)

Expected behavior

no errors, no warnings

pylint --version output

pylint 1.7.1, 
astroid 1.5.2
Python 2.7.13 (default, Dec 18 2016, 07:03:39) 
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)]

[erjiang]

This has hit us too. We are using a variable that is initialized to None, but then gets assigned to dict in a loop.

I think something like this will trigger it too:

points = [{"lat": 39, "lon": -92}, {"lat": 39.1, "lon": -92.1}]

furthest_west = None
for p in points:
    if furthest_west is None:
        furthest_west = p
    else:
        if p['lon'] < furthest_west['lon']:
            furthest_west = p

not sure how you would solve this, seems like the inferencer would have to go into the if/else clauses to see what might get assigned to the variable to figure out that it's Union(None, dict).