Inconsistent detection of undefined variable in try clause

[hemberger]

Steps to reproduce

When an undefined variable is in a try-clause, pylint does not report it as undefined, depending on which type of exception we're catching.

It fails to detect the undefined variable if the exception is bare or NameError:

try:
    bla
except:
    pass

try:
    bla
except NameError:
    pass

It correctly detects the undefined variable if the exception is Exception or some other derived exception that is not NameError:

try:
    bla
except Exception:
    pass

try:
    bla
except KeyError:
    pass

Current behavior

No error is raised (for bare exception and NameError)

Expected behavior

E0602: Undefined variable 'bla' (undefined-variable)

pylint --version output

pylint 2.4.3
astroid 2.3.3
Python 3.7.3 (default, Oct 7 2019, 12:56:13)
[GCC 8.3.0]

[PCManticore]

Thanks for the report. For NameError this is expected, as pylint takes a hint from the exception handler in figuring out if the variable is expected to be undefined or not. For instance this is useful when wanting to check particular features of the language, like the presence of a builtin (in Python 2 vs Python 3 scenario for example).

But I think we should still emit it for bare except, and only allow NameError to swallow undefined variables.