In languages such as Javascript, the incrementation of a for loop counter can be done by an operation, for instance :
for(i=1; i<N; i*=2)
would iterate on the powers of 2 lesser than N.
To achieve the same thing in Python we currently can't use range() because it increments by an integer (the argument "step"). An option is to build a generator like :
def gen(N):
i = 1
while i<=N:
yield i
i *= 2
then we can iterate on gen(N).
My proposal is that besides an integer, range() would accept a function as the "step" argument, taking the current counter as its argument and returning the new counter value. Here is a basic pure-Python implementation :
import operator
class Range:
def __init__(self, start, stop, incrementor):
self.start, self.stop = start,
stop
self.incrementor = incrementor
# Function to compare current counter and stop value : <= or >=
self.comp =
operator.ge if self.stop>self.start else operator.le
self.counter = None
def __iter__(self):
return self
def __next__(self):
if self.counter is None:
self.counter = self.start
else:
self.counter = self.incrementor(self.counter)
if self.comp(self.counter, self.stop):
raise StopIteration
return self.counter
Iterating on the powers of 2 below N would be done by :
for i in Range(1, N, lambda x:x*2)
I haven't seen this discussed before, but I may not have searched enough.
Any
opinions ?