Python assignment destructuring

Question

These three expressions seem to be equivalent:

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

Do they compile to the same code?

Which one is more pythonic?

Answer 1

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        

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).