[Tutor] Deleted dictionary length not reporting

[Steven D'Aprano]

On 17/07/13 12:55, Jim Mooney wrote:
> so I'm going back to just popping used items
> from a list, which was dirt-simple.

And also dirt-simple to get wrong, and inefficient as well.

list.pop has its uses, but I strongly recommend that you learn more "Pythonic" techniques that don't rely on modifying the list unnecessarily. For example, instead of something like this:


while some_list:
     process(some_list[0])  # work on the first item
     some_list.pop(0)  # and then drop it


this will be *much* more efficient, as well as easier to understand:

for item in some_list:
     process(item)


If you really need to clear the list, it's more efficient to clear it all at once at the end than to clear it item-by-item:

some_list[:] = []


Here's a question for you, to test your Python knowledge:

Assuming that some_list is already a list, what's the difference between these two lines, and under what circumstances why would you want to use the second one?

some_list = []
some_list[:] = []


(Tutors, please leave this one for the beginners to answer.)


-- 
Steven