How do I check if current code is part of a try-except-block?

Question

I'm debugging a function that I wrote as part of some form of plug-in framework. The function does not appear to be doing what it should, and I have the suspicion that, somewhere up the stack, someone is catching exceptions, or raise (either a very specific or a very generic) exception and test what happens (but if it's swallowed, it still doesn't tell me where). I could enter the debugger and inspect the source code at every stack level. Is there a more direct way to list any try-except blocks that the current code may be part of — specifically, the try-part of any such block?

This is, of course, exclusively for debugging purposes.

Answer 1

It's spectacularly possible I'm missing something here (I just eyeballed the dis.dis() output for the catcher function), but at least this catches simple cases of catching things on Python 3.7:

import sys
import dis


def are_we_being_caught():
    frame = sys._getframe(1)
    while frame:
        bytecode = dis.Bytecode(frame.f_code)
        except_stack = 0
        for instr in bytecode:
            if instr.opname == "SETUP_EXCEPT":  # Going into a try: except: block
                except_stack += 1
            elif instr.opname == "POP_EXCEPT":  # Exiting a try: except: block
                except_stack -= 1
            if instr.offset > frame.f_lasti:  # Past the current instruction, bail out
                break
        if except_stack:  # If we `break`ed in the middle of a SETUP/POP pair
            print(frame, "may be catching exceptions now")
        frame = frame.f_back


def catcher(fn):
    try:
        x = fn()
    except:
        x = None  # YOLO :D
    return x


def f1():
    return 8


def f2():
    are_we_being_caught()
    raise ValueError("foo")


print(catcher(f1))
print(catcher(f2))

outputs

8
<frame at 0x109d2d238, file 'so55729254.py', line 24, code catcher> may be catching exceptions now
None

Answer 2

That's a pretty difficult one: internally, each frame maintains a stack of blocks but I don't think there's any API to access it (let alone from Python). So you'd have to walk the stackframes, disassemble the code to infer the span of your try blocks (see the SETUP_EXCEPT and SETUP_FINALLY opcodes), and see if the "current line" of the stack frame falls within that block.