Comments on: There are more than one way to do it

By: tripu

tripu — Thu, 23 Apr 2009 12:34:12 +0000

The shortest one, no matter what!

By: lgs

lgs — Tue, 21 Apr 2009 18:56:14 +0000

Thanks for your replies, Andrew and Adomas!!

I love your solutions and they truly feel pythonic. Thanks for teaching me. However the method I post here was a simplified version of the real method. In the real one, I pass some arguments to the collector(destination) function that depends on the number of iterations.

Thanks again!

By: Adomas Paltanavicius

Adomas Paltanavicius — Sun, 19 Apr 2009 22:40:03 +0000

1 from itertools import chain, islice
2
3 for photo in islice(chain(*self.collectors), self.max):
4 self.add_photo(photo)
5
6 return self.get_photos()

By: Andrew Durdin

Andrew Durdin — Sun, 19 Apr 2009 21:32:18 +0000

As I was afraid, the indentation of that was lost. Here it is again with leading non-breaking spaces. I hope they work better:

1 def collect_photos(self, destination):
2 from itertools import islice

3      def photos_fetcher():
4          for collector in self.collectors:
5              for photo in collector(destination):
6                  yield photo

7 for photo_info in islice(photos_fetcher(), self.max):
8 self.add_photo(photo_info)

9 return self.get_photos()

By: Andrew Durdin

Andrew Durdin — Sun, 19 Apr 2009 21:31:14 +0000

Of these, none of them seem to me to quite as simple as they might be. The itertools module has quite a lot of tools to help with simple tasks like this.
Here I build a generator that yields photos sequentially for as long as possible; then use islice() to limit it to no more than self.max. If there are fewer photos than this, then that for loop will just end a little sooner:

1 def collect_photos(self, destination):
2 from itertools import islice

3 def photos_fetcher():
4 for collector in self.collectors:
5 for photo in collector(destination):
6 yield photo

7 for photo_info in islice(photos_fetcher(), self.max):
8 self.add_photo(photo_info)

9 return self.get_photos()

As a side note, you should rarely (in Python) need to manually increment a variable to count elements in an iterable; instead, use enumerate(), or itertools.izip() together with itertools.count() if you need more than 0-indexed incrementing.

“Then I tried to convert the for loops into while loops since basic computer science tell us that a while loop is the choice to make when the number of iterations is unknown.”

In Python, I’d actually argue in favour of using iterators/generators and for loops in preference to while loops, as the termination conditions are usually a lot clearer, and the resulting code is often more succint.