gistfile1.py

>>> def f1(y):
...  return set(x for x in y)
... 
>>> def f2(y):
...  return {x for x in y}
... 
>>> dis.dis(f1)
  2           0 LOAD_GLOBAL              0 (set)
              3 LOAD_CONST               1 (<code object <genexpr> at 0x10abecd30, file "<stdin>", line 2>)
              6 MAKE_FUNCTION            0
              9 LOAD_FAST                0 (y)
             12 GET_ITER            
             13 CALL_FUNCTION            1
             16 CALL_FUNCTION            1
             19 RETURN_VALUE        
>>> dis.dis(f2)
  2           0 LOAD_CONST               1 (<code object <setcomp> at 0x10ac14130, file "<stdin>", line 2>)
              3 MAKE_FUNCTION            0
              6 LOAD_FAST                0 (y)
              9 GET_ITER            
             10 CALL_FUNCTION            1
             13 RETURN_VALUE