Python赋值解构

Question

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()

他们编译成相同的代码吗？

哪一个更pythonic？

Answer 1

据说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        

所以他们都应该具有相同的效率.至于哪个是大多数Pythonic,它有点落后于观点,但我赞成第一个或(在较小程度上)第二个选项.使用方括号是令人困惑的,因为它看起来像你正在创建一个列表(虽然事实证明你不是).