Python isn't the only capability you're typically being evaluated for, though. A binary search tree is a very simple thing. I think it's reasonable to expect a candidate to come up with a basic implementation of a binary search tree, especially if you are giving him/she hints when he/she gets stuck -- an interview should be a two-way conversation. If you can't come up with something approaching a binary search tree in an hour and with my help, how can I expect you to design a reasonably complex system when the business needs it?
Now if you are asked to come up with a red black tree without any help, now that is a different story. A red black tree's implementation details are hard to derive given a set of requirements. A binary search tree, not so much.
Now if you are asked to come up with a red black tree without any help, now that is a different story. A red black tree's implementation details are hard to derive given a set of requirements. A binary search tree, not so much.