[Python-ideas] Pass a function as the argument "step" of range()
Ryan Gonzalez
rymg19 at gmail.com
Fri Jul 3 02:36:09 CEST 2015
I like the idea, but this would be nicer in a language with implicit currying so that your example could be:
for i in Range(1, N, (*2)):
...
Or in Haskell:
range' v a b f
| a == b = []
| otherwise = f a:range v a+v b f
range a b
| a > b = range' -1 a b
| a < b = range' 1 a b
| a == b = []
Since Python doesn't have this, the generator forms others showed would likely end up more concise.
On July 2, 2015 1:30:53 AM CDT, Pierre Quentel <pierre.quentel at gmail.com> wrote:
>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 ?
>
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Python-ideas mailing list
>Python-ideas at python.org
>https://mail.python.org/mailman/listinfo/python-ideas
>Code of Conduct: http://python.org/psf/codeofconduct/
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20150702/15505af6/attachment.html>
More information about the Python-ideas
mailing list