Debugging Snippet

Print all the parameters passed to a function and its return value:

from functools import wraps
 
def debug(func):
    @wraps(func)
    def wrapper_debug(*args, **kwargs):
        args_repr = [repr(a) for a in args]
        kwargs_repr = [f"{k}={v!r}" for k, v in kwargs.items()]
        signature = ", ".join(args_repr + kwargs_repr)
        print(f"Calling {func.__name__}({signature})")
        value = func(*args, **kwargs)
        print(f"{func.__name__!r} returned {value!r}")
        return value
    return wrapper_debug

Usage:

@debug
def my_func(a, b, c):
    return a + b + c

Result:

>>> my_func(1, 2, 3)
Calling my_func(1, 2, 3)
'my_func' returned 6
6

Note: There is a {v!r} in the code above. What it does is that it calls repr() on the value before interpolating it into the string. This is equivalent to doing f"{k}={repr(v)}".

I didn’t know about this until I read this in the docs.