Python赋值解构

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时间:2020-08-19 05:35:32  来源:igfitidea点击:

Python assignment destructuring

pythondestructuring

提问by sds

These three expressions seem to be equivalent:

这三个表达式似乎是等价的:

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

Do they compile to the same code?

它们编译成相同的代码吗?

Which one is more pythonic?

哪个更pythonic?

采纳答案by dano

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

根据dis,它们都被编译为相同的字节码:

>>> 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        

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).

所以它们都应该具有相同的效率。至于哪个是最 Pythonic 的,这在某种程度上取决于意见,但我更喜欢第一个或(在较小程度上)第二个选项。使用方括号令人困惑,因为看起来您正在创建一个列表(尽管事实证明您不是)。