Decompile code in the try...return...except format fail

[waaaagit]

A return statement between try and except makes decompilation fail to produce correct results.

$ python Python 3.11.1 (main, Sep 8 2025, 16:27:45) [GCC 8.3.0] on linux

def test():
    try:
        a = 1
    except:
        return False
    return False

The pyc file generated by the code above can be decompiled correctly.

def test():
    try:
        return 1
    except:
        return False
    return False

The pyc file generated by the code above can't be decompiled correctly.

[XinlongCS]

This is actually a funny case. The issue here is that once the return starts, the exception except clause can no longer trigger. Not even a frame-perfect KeyBoardInterrupt can actually trigger the except block. It's actually semantically equivalent to prune the unreachable code and just decompile the function as return 1. The reason why it fails the perfect decompilation test is that when we removed the unreachable code and updated the exception table, we didn't remove exception table entries, even when they ended up covering no instructions.

In #101, we updated the remove_instructions function to clean up those empty exception table entries, which allows the perfect decompilation test to pass here.

Thanks for the fun puzzle!

[waaaagit]

Thanks for your work.

I saw your commit 1d6222b

I have another two case, maybe more

def test(a,b,c):
    try:
        d=a/b
        return 1
    except:
        try:
            e=b/a
        except:
            f = b/c
            return 2
    return 3

def test(a,b,c):
    try:
        d=a/b
        return 1
    except:
        try:
            e=b/a
            return 2
        except:
            f = b/c
    return 3

The two cases above can't be decompiled correctly.