Code like this often happens:

l = []
while foo:
    #baz
    l.append(bar)
    #qux

This is really slow if you're about to append thousands of elements to your list, as the list will have to constantly be re-initialized to grow. (I understand that lists aren't just wrappers around some array-type-thing, but something more complicated. I think this still applies, though; let me know if not).

In Java, you can create an ArrayList with an initial capacity. If you have some idea how big your list will be, this will be a lot more efficient.

I understand that code like this can often be re-factored into a list comprehension. If the for/while loop is very complicated, though, this is unfeasible. Is there any equivalent for us python programmers?