[almostgotcaught]

yes there is: https://wiki.python.org/moin/UsingSlots

people really don't know enough about this to be talking about it with such confidence...

[dontlaugh]

I was pointing examples of the opposite, that JavaScript is less dynamic than Python.

There's lots of Python code out there that relies on not using slots. If you're making a JIT, you can't assume that all code is using slots.