Pythonic infinite for loop?
ryan at rfk.id.au
Fri Apr 15 04:34:17 CEST 2011
On Fri, 2011-04-15 at 12:10 +1000, Chris Angelico wrote:
> Apologies for interrupting the vital off-topic discussion, but I have
> a real Python question to ask.
> I'm doing something that needs to scan a dictionary for elements that
> have a particular beginning and a numeric tail, and turn them into a
> single list with some processing. I have a function parse_kwdlist()
> which takes a string (the dictionary's value) and returns the content
> I want out of it, so I'm wondering what the most efficient and
> Pythonic way to do this is.
> My first draft looks something like this. The input dictionary is
> called dct, the output list is lst.
> for i in xrange(1,10000000): # arbitrary top, don't like this
> except KeyError:
> I'm wondering two things. One, is there a way to make an xrange object
> and leave the top off? (Sounds like I'm risking the numbers
> evaporating or something.)
There is, use an infinite generator:
start += 1
for i in ints_from(1):
But why not just put the while loop inline:
i = 0
i += 1
It might be even easier to just iterate through the dictionary keys:
for k in sorted(dct.keys()):
> And two, can the entire thing be turned
> into a list comprehension or something? Generally any construct with a
> for loop that appends to a list is begging to become a list comp, but
> I can't see how to do that when the input comes from a dictionary.
You probably could, but I think it would hurt readability in this case:
lst = [parse_kwdlist(dct[k]) for k in sorted(dct.keys())
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