Opposite of any() function


The Python built-in function any(iterable) can help to quickly check if any bool(element) is True in a iterable type.

>>> l = [None, False, 0]
>>> any(l)
>>> l = [None, 1, 0]
>>> any(l)

But is there an elegant way or function in Python that could achieve the opposite effect of any(iterable)? That is, if any bool(element) is False then return True, like the following example:

>>> l = [True, False, True]
>>> any_false(l)
>>> True
Asked By: Ekeyme Mo



Write a generator expression which tests your custom condition. You’re not bound to only the default truthiness test:

any(not i for i in l)
Answered By: deceze

There is also the all function which does the opposite of what you want, it returns True if all are True and False if any are False. Therefore you can just do:

not all(l)
Answered By: Jack Aidley

Well, the implementation of any is equivalent to:

def any(iterable):
    for element in iterable:
        if element:
            return True
    return False

So, just switch the condition from if element to if not element:

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

Yes, of course this doesn’t leverage the speed of the built-ins any or all like the other answers do, but it’s a nice readable alternative.

You can do:

>>> l = [True, False, True]
>>> False in map(bool, l)

Recall that map in Python 3 is a generator. For Python 2, you probably want to use imap

Mea Culpa: After timing these, the method I offered is hands down the slowest

The fastest is not all(l) or not next(filterfalse(bool, it), True) which is just a silly itertools variant. Use Jack Aidleys solution.

Timing code:

from itertools import filterfalse

def af1(it):
    return not all(it)

def af2(it):
    return any(not i for i in it)   

def af3(iterable):
    for element in iterable:
        if not element:
            return True
    return False    

def af4(it):
    return False in map(bool, it)   

def af5(it):
    return not next(filterfalse(bool, it), True)    

if __name__=='__main__':
    import timeit   
    for i, l in enumerate([[True]*1000+[False]+[True]*999, # False in the middle
                           [False]*2000, # all False
                            [True]*2000], # all True
        print("case:", i)
        for f in (af1, af2, af3, af4, af5):
            print("   ",f.__name__, timeit.timeit("f(l)", setup="from __main__ import f, l", number=100000), f(l) )


case: 1
    af1 0.45357259700540453 True
    af2 4.538436588976765 True
    af3 1.2491040650056675 True
    af4 8.935278153978288 True
    af5 0.4685744970047381 True
case: 2
    af1 0.016299808979965746 True
    af2 0.04787631600629538 True
    af3 0.015038023004308343 True
    af4 0.03326922300038859 True
    af5 0.029870904982089996 True
case: 3
    af1 0.8545824179891497 False
    af2 8.786235476000002 False
    af3 2.448748088994762 False
    af4 17.90895140200155 False
    af5 0.9152941330103204 False
Answered By: dawg
Categories: questions Tags: , ,
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