Detect the same `if` conditions

[sobolevn]

Today I saw this code:

if isinstance(x, int):
    ...
elif isinstance(x, str):
    ...
elif isinstance(x, int): ...

The thing is that isinstance(x, int) is duplicated. And the second branch won't ever be called.

We need to detecct this kind of problems and report them.

[Dreamsorcerer]

Isn't this a case for mypy? It should warn that the 3rd statement is unreachable (if you've enabled that option).

[sobolevn]

Yes, mypy can catch some cases. But, not this one for example:

def some(x: int) -> None:
    if x == 1:
        ...
    elif x == 2:
        ...
    elif x == 1:
        ...

[orsinium]

Looking at the title, I thought about something like this:

if a:
 ...
if a:
 ...

Both blocks follow next to each other and have the same condition and so can be merged.

[sobolevn]

This is a different issue, I guess 🙂 We can detect similar conditions that go as the next statement.