scoping with lambda in loops

[Ian McMeans]

I was bitten by a bug today that depended on how lambda works. It took
me quite a while to realize what was going on.

First, I made multiple lambda functions inside a loop, each of which
depended on the current loop variable.

>>> a = []
>>> for index in range(5):
	a.append(lambda: index)


Now, see if you can guess what the output was for each of the
functions in the list a:
>>> a[0](), a[1](), a[2](), a[3](), a[4]()
I had expected it to be (0, 1, 2, 3, 4), but actually, it's:

(4, 4, 4, 4, 4)

This really surprised me. I guess what is happening is that each
lambda knows what the context of execution is where it was defined,
and doesn't actually evaluate until the function is called, and when
it does evaluate, it uses the current value of the variable. Is this
related to static scoping? A similar thing would happen if you defined
a nested function that used a variable declared in the outer function,
then changed that variable, and called the nested function.

Can someone recommend a way to code around this gotcha? I'm having
trouble. I want the functions created inside the loop to execute with
the value of the loop index at the moment when the function is made.