We don't call them "arrays".

It has nothing to do with whether the list is empty. It has nothing to do with lists at all. It's the behaviour of default arguments.

It happens at the time that the function object is created, which is during runtime.

You only notice because lists are mutable. You should already prefer not to mutate parameters, and it especially doesn't make sense to mutate a parameter that has a default value because the point of mutating parameters is that the change can be seen by the caller, but a caller that uses a default value can't see the default value.

The behaviour can be used intentionally. (I would argue that it's overused intentionally; people use it to "bind" loop variables to lambdas when they should be using `functools.partial`.)

If you're getting got by this, you're fundamentally expecting Python to work in a way that Pythonistas consider not to make sense.

Execution time, not parse time. It's a side effect of function declarations being statements that are executed, not the list/dict itself. It would happen with any object.

If you change this you break a common optimization:

https://github.com/python/cpython/blob/3.14/Lib/json/encoder...

Default value is evaluated once, and accessing parameter is much cheaper than global

there is PEP 671 for that, which introduces extra syntax for the behavior you want. people rely on the current behavior so you can't really change it