Python debug function

In Rust you find the dbg! macro that prints to what a given expression evaluates to. This on its own wouldn't be as helpful. Thus, additionally the macro returns the value of the evaluated expression.

It is possible to mimic this functionality in Python. You may find the original implementation on Raphael's blog. The one I use, is roughly:

import inspect
import sys
import typing

_ExpType = typing.TypeVar('_ExpType')


def dbg(exp: _ExpType) -> _ExpType:
    for frame in inspect.stack():
        line = frame.code_context[0]

        if 'dbg' in line:
            start = line.find('(') + 1
            end = end if (end := line.rfind(')')) >= 0 else len(line) 

            print(f'[{frame.filename}:{frame.lineno}] {line[start:end]} = {exp!r}', 
                  file=sys.stderr)
            break

    return exp

Whether in it's a *.py file or in a notebook, it works great. Exemplary output:

>>> a, b = 1, 2
... dbg(a + b)
[(...):2] a + b = 3
3