`return` event line missing when exception occurred

[yantaozhao]

When exception occurred, the return event is not recorded in snoop log. This leaves an unbalanced call-return pairs.

Expected behavior: all event should properly be recorded even though exception happened.

demo code:

import pysnooper

def bar(a, b):
    return a + b

def baz():
    try:
        x = 'hi' + 1  # exception here!
        return 1
    except:
        raise  # <- return event missing
    return -1

def foo():
    r = bar(2, 3)
    print(r)
    return r

@pysnooper.snoop(depth=2, normalize=True)
def main():
    foo()
    try:
        baz()
    except:
        pass

main()

In the above demo, return event in line 13 is not recorded like line 20 do. the call-return pair is broken.

[cool-RR]

Which versions of PySnooper and Python? And what OS?

[yantaozhao]

python 3.10, PySnooper 1.2.0, all platforms

[cool-RR]

Ah, it's possible that I have just caused this bug with this most recent version. I'll look into it.

[cool-RR]

If you're interested in writing a failing test case, that'll be helpful.

[yantaozhao]

commit a PR to fix this issue.

[cool-RR]

Can you explain why there should be a return line when an exception is raised? Can you explain what practical problem it causes that this line doesn't exist?

[yantaozhao]

Can you explain why there should be a return line when an exception is raised?

No matter exception raised or not, all return event should be recorded because it really happened. Additionally it make things easy to write a log analyser as the call-return pairs are balanced.

Can you explain what practical problem it causes that this line doesn't exist?

For log readable, consider below example:

import pysnooper

def bar(a, b):
    return a + b

def baz():
    try:
        x = 'hi' + 1  # exception here!
        return 1
    except:
        raise
    finally:  # <-do something and output
        a=1
        b=2
        c=a+b
        foo()
    return -1

def foo():
    r = bar(2, 3)
    print(r)
    return [8]

@pysnooper.snoop(depth=9, normalize=True)
def main():
    try:
        baz()
    except:
        pass

main()

if return 18 was not recorded, athough it can, but will spend more time to find that the code ran to and returned from line 18.

[alexmojaki]

It make things easy to write a log analyser

It sounds like you might prefer using something like https://github.com/ionelmc/python-hunter. Or just writing your own function for sys.settrace.

[cool-RR]

@yantaozhao Sorry, I'm not seeing the practical usage here. It actually sounds misleading to write "return" when a function exited because of an exception rather than returned a value. I'm not sure what your use case is, but it sounds like it's a very niche use case that's not worth compromising for.