B001 misses some bare excepts

B001 and Flake8/pycodestyle E722 both check for bare_except, but B001 misses a lot of cases that E722 finds.

We noticed this when we tried running an internal tool that looks for overlaps in checks – we are writing some of our own and don’t want to overlap – and found that every time B001 fires E722 also fires; but the reverse is not true.

Tool output: B001 (6786) <-> E722 (34093): 13572 occurred at same line+path B001 implies E722: 100% E722 implies B001: 19%

I took a look at the implementations for B001 and E722 and found that bugbear uses the AST and E722 uses a regex:

Bugbear implementation uses AST.

def visit_ExceptHandler(self, node):
    if node.type is None:
        self.errors.append(B001(node.lineno, node.col_offset))
    self.generic_visit(node)

Flake8 implementation uses regex.

def bare_except(logical_line, noqa):
    if noqa:
        return

    regex = re.compile(r"except\s*:")
    match = regex.match(logical_line)
    if match:
        yield match.start(), "E722 do not use bare 'except'"

From the implementation, it looks like B001 and E722 should hit the same locations every time.

We have a platform that lets us run static analysis over a bunch of open source repositories at the same time, so I ran vanilla flake8 and bugbear at the same time to see if there was a pattern, but one wasn’t immediately obvious.

I thought this might be related to forgetting to call visit or something like that (I’ve been bitten by that before!) but the reason for this disparity wasn’t clear to me… so I’m making this issue. Feel free to reach out to me if you have any other questions!

Here are some examples:

[ambv]

+1

[cooperlees]

Maybe it’s time to just drop our “limited” Python 2 support all together. It’s past midpoint 2020.