Python Variable Exchange performance optimization

New in many ways Python performance optimizations see the value of swapping two variables can be used

A, B = b,a

This can improve performance

>>> from Timeit import timer>>> Timer ("t=a;a=b;b=t", "a=1;b=2"). Timeit () 0.06279781319366587> >> Timer ("A,b=b,a", "a=1;b=2"). Timeit () 0.0378979925538232>>>

From the running time, it really saved half the time.

Get Python bytecode with dis

>>> def func (): ...     b = b,a...>>> Import dis>>> Dis.dis (func)  2           0 load_fast                0 (b)              3 load_fast                1 (a)              6 rot_two              7 store_fast               1 (a)             store_fast               0 (b)             load_const               0 (None)             RETURN _value>>>

It can be seen that the main rot_two instruction is the credit:

Consult a Python document for instructions such as Rot_two Rot_three Rot_four, which can be exchanged directly for two variables, three variables, and four variable values

Read the ceval.c file in the source code of python3.4 to see:

       TARGET (rot_two) {            Pyobject *top = Top ();            Pyobject *second = second ();            Set_top (second);            Set_second (top);            Fast_dispatch ();        }        TARGET (rot_three) {            Pyobject *top = Top ();            Pyobject *second = second ();            Pyobject *third = third ();            Set_top (second);            Set_second (third);            Set_third (top);            Fast_dispatch ();        }

Is that the specific C language of these instructions implements the
After all, the speed is fast or because A, B = B,a is all using the pointer operation

Python Variable Exchange performance optimization