python - Is list pass by value or by reference?

It’s passed by value of reference. So modifications to the object can be seen outside the function, but assigning the variable to a new object does not change anything outside the function.

It’s essentially the same as passing a pointer in C, or a reference type in Java.

The result of the += case is because that operator actually modifies the list in place, so the effect is visible outside the function. lst.append() is also an in-place operation, which explains your last case.