Isn't this pretty obvious if you spent more than three weeks writing python? There are lots tricks, but these listed here seem relevant to all languages. There is an almost an incountable amount of ways to write bad and slow python code that are not as obvious.

I remember the day I realized how much I dislike python. I have never had it click for me, despite writing it in and off since the python 2.0. There are always some new arbitrary places for it to bite you, and it always feels a little yucky. And then one day I saw something like this:

    # b is not defined here
    if blahblah():
        b = gronk()
    # might raise an exception
    do_stuff(b)

That tingles in all the wrong places. Ruby has other issues, but the core is still feels elegant. I still prefer scheme, though.

Edit: and maybe someone can explain to me why anyone would make it so that the simplest way to iterate through a collection is not the fastest? This is the case for most languages, but it still feels dumb. Just allow a slightly more obtuse syntax like

    for a in b<list>

and make that case just as fast as doing it with a while loop. The iterator protocol is imho for when we frankly don't know/care what we are iterating over, or when we elwant to be generic, or when the data structure can't expose the most efficient way of doing it (like a tree). There is no reason why for a in b: should be slower than while when b is a list or string.