Does Python's `all` function use short circuit evaluation?

Question

I wish to use the Python all() function to help me compute something, but this something could take substantially longer if the all() does not evaluate as soon as it hits a False. I'm thinking it probably is short-circuit evaluated, but I just wanted to make sure. Also, is there a way to tell in Python how the function gets evaluated?

---

_{Editor's note: Because any and all are functions, their arguments must be evaluated before they are called. That often creates the impression of no short-circuiting - but they do still short-circuit.}

_{To make sure that the short-circuiting can be effective, pass a generator expression, or other lazily evaluated expression, rather than a sequence. See Lazy function evaluation in any() / all() for details. Similarly, to force evaluation up-front, build a list or tuple explicitly; see How to prevent short-circuit evaluation? .}

Answer 1

Yes, it short-circuits:

>>> def test():
...     yield True
...     print('one')
...     yield False
...     print('two')
...     yield True
...     print('three')
...
>>> all(test())
one
False

From the docs:

Return True if all elements of the iterable are true (or if the iterable is empty). Equivalent to:

def all(iterable):
    for element in iterable:
        if not element:
            return False
    return True

So when it returns False, then the function immediately breaks.