pythontips7.py

In [25]: dis.dis("t[a] += b")                                                                                                                                                                                       
  1           0 LOAD_NAME                0 (t)
              2 LOAD_NAME                1 (a)
              4 DUP_TOP_TWO
              6 BINARY_SUBSCR
              8 LOAD_NAME                2 (b)
             10 INPLACE_ADD --> (value in t[a]) += b --> succeeds because list is mutable
             12 ROT_THREE
             14 STORE_SUBSCR --> Assign t[a] = our list --> Fails, t[a] is immutable.
             16 LOAD_CONST               0 (None)
             18 RETURN_VALUE