Question

What is the idiomatic Python way to test if all elements in a collection satisfy a condition? (The .NET All() method fills this niche nicely in C#.)

There’s the obvious loop method:

all_match = True
for x in stuff:
    if not test(x):
        all_match = False
        break

And a list comprehension could do the trick, but seems wasteful:

all_match = len([ False for x in stuff if not test(x) ]) > 0

There’s got to be something more elegant… What am I missing?

Answer 1

all_match = all(test(x) for x in stuff)

This short-circuits and doesn’t require stuff to be a list — anything iterable will work — so has several nice features.

There’s also the analogous

any_match = any(test(x) for x in stuff)