This would be similar to 'key' argument already available for min(), max() and sorted() and would let user decide what must be considered True and what not.

Some use cases:

all(a, b, c, ... key=callable)

all(a, b, c, ... key=lambda x: isinstance(x, int))

any(a, b, c, ... key=lambda x: x < 10)

a = b = c = None

for x in foo:

    if cond1:

         a = 0

    elif cond2:

         b = 0

    elif cond3:

         c = 0

# meaning all cond* has been satisfied and it's ok to consider 0 a meaningful value

assert all(a, b, c, key=lambda x: x != None)   

Thoughts?

--- Giampaolo