[masklinn]

> Very similar structures, with very different memory requirements and access speeds. I can count on one hand with no fingers the number of times I've seen an array used.

That is obvious when you actually check the access speed of arrays and find out it is about half that of lists on small integers (under 256), and worse on non-small integers. That is literally the opposite trade off of what you want in 99.99% of cases.

Deques are even less of a consideration, they’re unrolled linked lists so random access is impossible and iteration is slower, you use a deque when you need a deque (or at least a fifo), aka when you need to routinely manipulate the head of the collection.

[sgarland]

It depends on your constraints. If you’re limited by RAM, arrays make a lot of sense for certain applications. If you need Python’s buffer protocol, again, they make a lot of sense.

As to deques, yes, they have specific uses, and being slightly smaller isn’t usually a selling point for them. My point was that I have seen many cases where an incorrect data structure was used, because a list or dict was “good enough.” And sure, they generally are, but if the language ships with other options, why wouldn’t you explore those?