Credit: Jon Dyte
You need to know whether all items in a sequence satisfy a certain predicate or if only some of them do.
The simplest approach for either problem is to loop on the sequence
and return a result as soon as it’s known, just as
the and
and or
Python operators
short-circuit logical evaluation:
def every (pred, seq): """ true if pred(x) is true for all x in seq, else false """ for x in seq: if not pred(x): return 0 return 1 def any (pred, seq): """ false if pred(x) is false for all x in seq, else true """ for x in seq: if pred(x): return 1 return 0
Often, it is useful to know whether all elements of a sequence meet
certain criteria or if only some do. The two functions
every
and any
do just that, with the simplest, and thus
clearest, approach:
>>> every(lambda c: c > 5, (6, 7, 8, 9)) 1 >>> every(lambda c: c > 5, (6, 4, 8, 9)) 0 >>> any(lambda c: c > 5, (6, 7, 8, 9)) 1 >>> any(lambda c: c < 5, (6, 7, 8, 9)) 0
If you want to get fancy, here are two more techniques (perhaps with some performance gain, though you shouldn’t take my word for it—always measure performance for the specific cases you need):
def every(pred, seq): return len(seq) == len(filter(pred, seq)) def any(pred, seq): return len(filter(pred, seq))
or:
import operator def every(pred, seq): return reduce(operator.and_, map(pred, seq)) def any(pred, seq): return reduce(operator.or_, map(pred, seq))
Functional forms are elegant and often fast, as long as they do not
involve a lambda
.