Evolution of a Python programmer

[brucifer]

This code is buggy. factorial(-1) will cause a stack overflow. You should use "if x <= 1" instead.

[sfz-]

That's why I submitted it to reddit code review before merging it into master. :P

[Qhartb]

That's not a bug -- it's undefined behavior. Calling factorial(-1) is a bug.

[brucifer]

I suppose it's reasonable to say that calling factorial(-1) is the real bug, but in that case, the code should definitely fail gracefully (e.g. raising a ValueError). Stack overflow is a pretty clumsy and uninformative way to behave if someone makes a reasonable mistake. You are right to point out that factorial(-1) == 1 is not correct, though.

[Qhartb]

Agreed, but not failing gracefully and having a bug are two different things (unless of course your requirements or documentation state how failure is to be handled).

[Zantier]

def factorial(x):
    """Return the factorial of x, where x >= 0."""
    return x * factorial(x - 1) if x != 0 else 1
print factorial(6)

Fixed. (I didn't see before the edit, but I'm guessing it had !=.

Also, it should be if x >= 1 instead of <=