Python作业解构 [英] Python assignment destructuring

问题描述

这三个表达式似乎是等效的:

These three expressions seem to be equivalent:

a,b,c = line.split()
(a,b,c) = line.split()
[a,b,c] = line.split()

它们是否编译为相同的代码?

Do they compile to the same code?

哪个是更pythonic的?

Which one is more pythonic?

推荐答案

根据 dis ，它们都被编译为相同的字节码:

According to dis, they all get compiled to the same bytecode:

>>> def f1(line):
...  a,b,c = line.split()
... 
>>> def f2(line):
...  (a,b,c) = line.split()
... 
>>> def f3(line):
...  [a,b,c] = line.split()
... 
>>> import dis
>>> dis.dis(f1)
  2           0 LOAD_FAST                0 (line)
              3 LOAD_ATTR                0 (split)
              6 CALL_FUNCTION            0
              9 UNPACK_SEQUENCE          3
             12 STORE_FAST               1 (a)
             15 STORE_FAST               2 (b)
             18 STORE_FAST               3 (c)
             21 LOAD_CONST               0 (None)
             24 RETURN_VALUE        
>>> dis.dis(f2)
  2           0 LOAD_FAST                0 (line)
              3 LOAD_ATTR                0 (split)
              6 CALL_FUNCTION            0
              9 UNPACK_SEQUENCE          3
             12 STORE_FAST               1 (a)
             15 STORE_FAST               2 (b)
             18 STORE_FAST               3 (c)
             21 LOAD_CONST               0 (None)
             24 RETURN_VALUE        
>>> dis.dis(f3)
  2           0 LOAD_FAST                0 (line)
              3 LOAD_ATTR                0 (split)
              6 CALL_FUNCTION            0
              9 UNPACK_SEQUENCE          3
             12 STORE_FAST               1 (a)
             15 STORE_FAST               2 (b)
             18 STORE_FAST               3 (c)
             21 LOAD_CONST               0 (None)
             24 RETURN_VALUE        

因此，它们都应具有相同的效率.至于哪个是最Python化的，这有点可取，但是我会选择第一个选项(或在较小程度上)选择第二个选项.使用方括号会造成混淆，因为看起来您正在创建列表(尽管事实并非如此).

So they should all have the same efficiency. As far as which is most Pythonic, it's somewhat down to opinion, but I would favor either the first or (to a lesser degree) the second option. Using the square brackets is confusing because it looks like you're creating a list (though it turns out you're not).

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