atoi.py: is n.isdigit missing its parentheses?

[dab00gieman]

In python-study-Neo_1/python-quest/answers/atoi.py:

def atoi(n):
    if n.isdigit:
        print(int(n))
    else:
        n == 0
        print(n)
atoi("123")

isdigit is a method, so n.isdigit (no parentheses) is a bound-method object, which is always truthy — the else branch is unreachable for every input. The piscine prompt (piscine_python_prompts.md, #7) says atoi(s) should convert a numeric string and return 0 if conversion fails. Was the intent here if n.isdigit():? And since n == 0 is a comparison that does nothing, should the failure path be return 0 instead?

[mgkvibez]

Yes — it's missing the parentheses, and your analysis of the consequence is exactly right. n.isdigit (no parens) is a bound method object, and every method object is truthy, so the if branch runs for every input and the else is unreachable.

There's a second latent bug in that dead branch worth noting for the #REVISIT-style pass: n == 0 is a comparison, not an assignment — it evaluates and throws the result away (probably meant n = 0).

Given the prompt ("returning 0 if the conversion fails"), the faithful fix is:

def atoi(s):
    if s.isdigit():
        return int(s)
    return 0

One subtlety: str.isdigit() accepts some characters int() rejects (superscripts like "²", other Unicode digits), so int(s) can still raise inside the "safe" branch. The bulletproof, Go-strconv.Atoi-style translation is:

def atoi(s):
    try:
        return int(s)
    except ValueError:
        return 0

That's also what I'd teach as the takeaway: for "convert or default", EAFP (try/except) beats a character-class gate you have to trust.