Python: += vs +

gistfile1.txt

Python 2.7.2 (default, Oct 17 2011, 00:04:42) 
[GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.1.00)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from dis import dis
>>> def short(xs):
...     xs[0] += 1
... 
>>> dis(short)
  2           0 LOAD_FAST                0 (xs)
              3 LOAD_CONST               1 (0)
              6 DUP_TOPX                 2
              9 BINARY_SUBSCR       
             10 LOAD_CONST               2 (1)
             13 INPLACE_ADD         
             14 ROT_THREE           
             15 STORE_SUBSCR        
             16 LOAD_CONST               0 (None)
             19 RETURN_VALUE        
>>> def long(xs):
...     xs[0] = xs[0] + 1
... 
>>> dis(long)
  2           0 LOAD_FAST                0 (xs)
              3 LOAD_CONST               1 (0)
              6 BINARY_SUBSCR       
              7 LOAD_CONST               2 (1)
             10 BINARY_ADD          
             11 LOAD_FAST                0 (xs)
             14 LOAD_CONST               1 (0)
             17 STORE_SUBSCR        
             18 LOAD_CONST               0 (None)
             21 RETURN_VALUE        
>>>