> The usually recommended alternative is to make a new list of
> things not deleted. But one can do this in-place by writing
> the new list on top of the old by using a explicit second
> index to move items just once.
I don't think we should send users down this path. Better to stick with high level, easy-to-implement and performant suggestions:
"""
To edit a list in-place it is often simplest and fastest to replace the entire list:
colors[:] = [color for color in colors if websafe(color)]
This makes a single pass through the list and efficiently builds a new list. The colors[:] then replaces the entire contents of the original list with the new list
"""
Besides being easy to get right, this is likely to be *much* faster than tracking two indicies to manipulate the array in-place. Slice operations run at the speed of a C memcpy (plus the ref count changes) and don't involve creating and destroying integer objects for indexing.