def gcd(x, y):
while(y): x, y = y, x % y
return x
The function above returns the greatest common divisor of two numbers. Why is y used as the condition in the while loop?
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2 Answers
The expression in a while statement will be evaluated as a boolean. An integer of 0 will evaluate to False, everything else will evaluate to True.
Your statement is equivalent to while y != 0:
Comments
This is used because the x % y will reduce y to the remainder of x / y (also called modulo) with each iteration of the loop. So the loop will execute as long as y 'is true' or in other words as long as y has a value that is not None or zero.
7 Comments
Tim Roberts
Well, it's never going to be "null". Python doesn't even have that. "As long as y has a value that is not zero" would be more accurate.
sog
My understanding is that null == 0 == False in Python but you are absolutely correct from a formal, mathematical perspective. So thank you for your clarification!
Tim Roberts
Python has
None, but not "null". If we're being picky, there are a whole set of things that are "false-ish", all of which work as Booleans.
Mark Ransom
Your latest edit isn't wrong (except for misspelling
None) but it's a little misleading since there's no way y could be None.
Matthias
@sog Your assumption that "null == 0 == False" is false, even if we use "None == 0 == False". You can check that with a simple
print(None == 0). |