How to unpack Tuple containing bool and str for assert

Question

Is there a way to unpack a tuple containing boolean and custom message and apply assert on it in single line single statement?

def test_numbers(a,b):
    if a==b:
        return True,"Are Equal"
    return False, "Not equal"

res, st = test_numbers(1,2)
assert res,st

Then tried the following, which didn’t work

assert *test_numbers(1,2)

same for:

assert (*test_numbers(1,2))

No, you can't unpack in a statement. What you have is as close as you can get. — jonrsharpe, Jul 28 '21 at 12:53
[relevant](https://stackoverflow.com/q/13390401/12671057), especially the accepted answer. — Kelly Bundy, Jul 28 '21 at 13:01
I think you are trying to check all items of your tuple are truthy, you migh use `all` : `assert all(test_numbers(1,2))` — vctrd, Aug 03 '22 at 18:33

score 3 · Answer 1 · answered Jul 28 '22 at 12:06

3

Solved by Walrus operator for `python >= 3.8`

https://realpython.com/python-walrus-operator/ Finally, this issue can be settled. The walrus operators := purpose is exactly to avoid double computation.

def check_numbers(a,b):
    if a==b:
        return True,"Are Equal"
    return False, "Not equal"

if __name__ == "__main__":
    assert (res:=check_numbers(1, 2))[0], res[1]

answered Jul 28 '22 at 12:06

Markus Dutschke

9,341
4
63
58

I'd rather add a function call that does `assert cond, msg` and call it like `validate(*check_numbers(1,2))` – Verthais Aug 02 '22 at 14:49

score 1 · Answer 2 · edited Aug 11 '22 at 02:13

One can go the detour over a custom assert function, but there should be a nicer way.

At least this solution gives the generated error message and is not called, when optimization (-> __debug__ == False) is on.

def check_numbers(a,b):
    if a==b:
        return True,"Are Equal"
    return False, "Not equal"

def custom_assert(cond, msg):
    # https: // docs.python.org / 3 / reference / simple_stmts.html  # the-assert-statement
    if __debug__:
        if not cond: raise AssertionError(msg)

if __name__ == "__main__":
    custom_assert(*check_numbers(1, 2))

score -1 · Answer 3 · answered Jul 28 '21 at 14:54

-1

assert test_numbers(1,2)[0]

Tuples can be indexed because they are iterables.

You don't need the 2nd value, do you ?

answered Jul 28 '21 at 14:54

cisco.prog

49
4

How to unpack Tuple containing bool and str for assert

3 Answers3

Solved by Walrus operator for python >= 3.8

Solved by Walrus operator for `python >= 3.8`