list_comp_is_a_for_loop.py

>>> import dis
>>> def regular_loop(source):
...     result = []
...     for x in result:
...         result.append(x**2)
...     return result
...
>>> def list_comp(source):
...     result = [x**2 for x in source]
...     return result
...
>>> dis.dis(regular_loop)
  2           0 BUILD_LIST               0
              2 STORE_FAST               1 (result)

  3           4 SETUP_LOOP              26 (to 32)
              6 LOAD_FAST                1 (result)
              8 GET_ITER
        >>   10 FOR_ITER                18 (to 30)
             12 STORE_FAST               2 (x)

  4          14 LOAD_FAST                1 (result)
             16 LOAD_METHOD              0 (append)
             18 LOAD_FAST                2 (x)
             20 LOAD_CONST               1 (2)
             22 BINARY_POWER
             24 CALL_METHOD              1
             26 POP_TOP
             28 JUMP_ABSOLUTE           10
        >>   30 POP_BLOCK

  5     >>   32 LOAD_FAST                1 (result)
             34 RETURN_VALUE
>>> dis.dis(list_comp)
  2           0 LOAD_CONST               1 (<code object <listcomp> at 0x10d69f0c0, file "<stdin>", line 2>)
              2 LOAD_CONST               2 ('list_comp.<locals>.<listcomp>')
              4 MAKE_FUNCTION            0
              6 LOAD_FAST                0 (source)
              8 GET_ITER
             10 CALL_FUNCTION            1
             12 STORE_FAST               1 (result)

  3          14 LOAD_FAST                1 (result)
             16 RETURN_VALUE

Disassembly of <code object <listcomp> at 0x10d69f0c0, file "<stdin>", line 2>:
  2           0 BUILD_LIST               0
              2 LOAD_FAST                0 (.0)
        >>    4 FOR_ITER                12 (to 18)
              6 STORE_FAST               1 (x)
              8 LOAD_FAST                1 (x)
             10 LOAD_CONST               0 (2)
             12 BINARY_POWER
             14 LIST_APPEND              2
             16 JUMP_ABSOLUTE            4
        >>   18 RETURN_VALUE