> What the precise difference (semantics and speed) is between the
> BINARY_ADD and INPLACE_ADD opcodes, I dunno. Look in the Python source
> code or maybe someone knows it from memory :-)
>
> Irmen
>
from Python/ceval.c:
1316 case BINARY_ADD:
1317 w = POP();
1318 v = TOP();
1319 if (PyInt_CheckExact(v) && PyInt_CheckExact(w)) {
1320 /* INLINE: int + int */
1321 register long a, b, i;
1322 a = PyInt_AS_LONG(v);
1323 b = PyInt_AS_LONG(w);
1324 /* cast to avoid undefined behaviour
1325 on overflow */
1326 i = (long)((unsigned long)a + b);
1327 if ((i^a) < 0 && (i^b) < 0)
1328 goto slow_add;
1329 x = PyInt_FromLong(i);
1330 }
1331 else if (PyString_CheckExact(v) &&
1332 PyString_CheckExact(w)) {
1333 x = string_concatenate(v, w, f, next_instr);
1334 /* string_concatenate consumed the ref to v */
1335 goto skip_decref_vx;
1336 }
1337 else {
1338 slow_add:
1339 x = PyNumber_Add(v, w);
1340 }
1341 Py_DECREF(v);
1342 skip_decref_vx:
1343 Py_DECREF(w);
1344 SET_TOP(x);
1345 if (x != NULL) continue;
1346 break;
1532 case INPLACE_ADD:
1533 w = POP();
1534 v = TOP();
1535 if (PyInt_CheckExact(v) && PyInt_CheckExact(w)) {
1536 /* INLINE: int + int */
1537 register long a, b, i;
1538 a = PyInt_AS_LONG(v);
1539 b = PyInt_AS_LONG(w);
1540 i = a + b;
1541 if ((i^a) < 0 && (i^b) < 0)
1542 goto slow_iadd;
1543 x = PyInt_FromLong(i);
1544 }
1545 else if (PyString_CheckExact(v) &&
1546 PyString_CheckExact(w)) {
1547 x = string_concatenate(v, w, f, next_instr);
1548 /* string_concatenate consumed the ref to v */
1549 goto skip_decref_v;
1550 }
1551 else {
1552 slow_iadd:
1553 x = PyNumber_InPlaceAdd(v, w);
1554 }
1555 Py_DECREF(v);
1556 skip_decref_v:
1557 Py_DECREF(w);
1558 SET_TOP(x);
1559 if (x != NULL) continue;
1560 break;
As for using Integers, the first case (line 1319 and 1535) are true and
there is no difference in Code. However, Python uses a huge switch-case
construct to execute it's opcodes and INPLACE_ADD cames after
BINARY_ADD, hence the difference in speed.
To be clear, this is nothing you should consider when writing fast code.
Complexity wise they both are the same.
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