It depends on which scope you define it at. Within the python interpreter, and the guarantees it gives, it is one of the definitions. However, at a higher level, the definition is really to give one variable the value of one list appended to another; without knowing how python works, you can't guarantee that it will be a new list.
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That isn't an undefined side-effect, that's the definition of the operation.
It depends on which scope you define it at. Within the python interpreter, and the guarantees it gives, it is one of the definitions. However, at a higher level, the definition is really to give one variable the value of one list appended to another; without knowing how python works, you can't guarantee that it will be a new list.