For loop

gistfile1.txt

In [1]: import dis

In [2]: for i in range(10):
   ...:     print(i)
   ...:     
0
1
2
3
4
5
6
7
8
9

In [3]: def f():
   ...:     for i in range(10):
   ...:         print(i)
   ...:         

In [4]: dis.dis(f)
  2           0 SETUP_LOOP              30 (to 33)
              3 LOAD_GLOBAL              0 (range)
              6 LOAD_CONST               1 (10)
              9 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
             12 GET_ITER
        >>   13 FOR_ITER                16 (to 32)
             16 STORE_FAST               0 (i)

  3          19 LOAD_GLOBAL              1 (print)
             22 LOAD_FAST                0 (i)
             25 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
             28 POP_TOP
             29 JUMP_ABSOLUTE           13
        >>   32 POP_BLOCK
        >>   33 LOAD_CONST               0 (None)
             36 RETURN_VALUE

--------------------------------------------------------------------
./Python/ceval.c, GET_ITER/FOR_ITER implementation:

        TARGET(GET_ITER) {
            /* before: [obj]; after [getiter(obj)] */
            PyObject *iterable = TOP();
            PyObject *iter = PyObject_GetIter(iterable);
            Py_DECREF(iterable);
            SET_TOP(iter);
            if (iter == NULL)
                goto error;
            PREDICT(FOR_ITER);
            DISPATCH();
        }

        PREDICTED_WITH_ARG(FOR_ITER);
        TARGET(FOR_ITER) {
            /* before: [iter]; after: [iter, iter()] *or* [] */
            PyObject *iter = TOP();
            PyObject *next = (*iter->ob_type->tp_iternext)(iter);
            if (next != NULL) {
                PUSH(next);
                PREDICT(STORE_FAST);
                PREDICT(UNPACK_SEQUENCE);
                DISPATCH();
            }
            if (PyErr_Occurred()) {
                if (!PyErr_ExceptionMatches(PyExc_StopIteration))
                    goto error;
                else if (tstate->c_tracefunc != NULL)
                    call_exc_trace(tstate->c_tracefunc, tstate->c_traceobj, tstate, f);
                PyErr_Clear();
            }
            /* iterator ended normally */
            STACKADJ(-1);
            Py_DECREF(iter);
            JUMPBY(oparg);
            DISPATCH();
        }