Oftentimes the case arises where one would need to loop indefinitely until a certain condition has been attained. For example, if I want keep collecting random integers until I find a number == n, following which I break. I'd do this:
import random
rlist = []
n = ...
low, high = ..., ...
while True:
num = random.randint(low, high)
if num == n:
break
rlist.append(num)
And this works, but is quite clunky. There is a much more pythonic alternative using iter:
iter(o[, sentinel])
Return an iterator object. The first argument is interpreted very differently depending on the presence of the second argument. [...] If the second argument, sentinel, is given, then o must be a callable object. The iterator created in this case will call o with no arguments for each call to its
next()method; if the value returned is equal to sentinel, StopIteration will be raised, otherwise the value will be returned.
The loop above can be replaced with
import random
from functools import partial
f = partial(random.randint, low, high)
rlist = list(iter(f, 10))
To extend this principle to lists that have already been created, a slight change is needed. I'll need to define a partial function like this:
f = partial(next, iter(x)) # where x is some list I want to keep taking items from until I hit a sentinel
The rest remains the same, but the main caveat with this approach versus the while loop is I cannot apply generic boolean conditions.
For example, I cannot apply a "generate numbers until the first even number greater than 1000 is encountered".
The bottom line is this: Is there another alternative to the while loop and iter that supports a callback sentinel?
