comp.py

In [14]: dis(x)
  2           0 BUILD_LIST               0
              3 LOAD_GLOBAL              0 (range)
              6 LOAD_CONST               1 (10)
              9 CALL_FUNCTION            1
             12 GET_ITER            
        >>   13 FOR_ITER                16 (to 32)
             16 STORE_FAST               0 (x)
             19 LOAD_FAST                0 (x)
             22 LOAD_CONST               2 (1)
             25 BINARY_ADD          
             26 LIST_APPEND              2
             29 JUMP_ABSOLUTE           13
        >>   32 RETURN_VALUE  

for.py

def x():
    return [x + 1 for x in range(10)]

def y():
    a = []
    for x in range(10):
        a.append(x+1)
    return a

forloop.py

In [17]: dis(y)
  2           0 BUILD_LIST               0
              3 STORE_FAST               0 (a)

  3           6 SETUP_LOOP              37 (to 46)
              9 LOAD_GLOBAL              0 (range)
             12 LOAD_CONST               1 (10)
             15 CALL_FUNCTION            1
             18 GET_ITER            
        >>   19 FOR_ITER                23 (to 45)
             22 STORE_FAST               1 (x)

  4          25 LOAD_FAST                0 (a)
             28 LOAD_ATTR                1 (append)
             31 LOAD_FAST                1 (x)
             34 LOAD_CONST               2 (1)
             37 BINARY_ADD          
             38 CALL_FUNCTION            1
             41 POP_TOP             
             42 JUMP_ABSOLUTE           19
        >>   45 POP_BLOCK           

  5     >>   46 LOAD_FAST                0 (a)
             49 RETURN_VALUE