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bpo-35900: Add a state_setter arg to save_reduce (GH-12588)

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Allow reduction methods to return a 6-item tuple where the 6th item specifies a
custom state-setting method that's called instead of the regular
``__setstate__`` method.
This commit is contained in:
Pierre Glaser 2019-05-08 21:40:25 +02:00 • committed by Antoine Pitrou
parent 39889864c0
commit 65d98d0f53
5 changed files with 114 additions and 15 deletions
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48
Modules/_pickle.c
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@ -3662,6 +3662,7 @@ save_reduce(PicklerObject *self, PyObject *args, PyObject *obj)
PyObject *state = NULL;
PyObject *listitems = Py_None;
PyObject *dictitems = Py_None;
PyObject *state_setter = Py_None;
PickleState *st = _Pickle_GetGlobalState();
Py_ssize_t size;
int use_newobj = 0, use_newobj_ex = 0;
@ -3672,14 +3673,15 @@ save_reduce(PicklerObject *self, PyObject *args, PyObject *obj)
const char newobj_ex_op = NEWOBJ_EX;
size = PyTuple_Size(args);
if (size < 2 || size > 5) {
if (size < 2 || size > 6) {
PyErr_SetString(st->PicklingError, "tuple returned by "
"__reduce__ must contain 2 through 5 elements");
"__reduce__ must contain 2 through 6 elements");
return -1;
}
if (!PyArg_UnpackTuple(args, "save_reduce", 2, 5,
&callable, &argtup, &state, &listitems, &dictitems))
if (!PyArg_UnpackTuple(args, "save_reduce", 2, 6,
&callable, &argtup, &state, &listitems, &dictitems,
&state_setter))
return -1;
if (!PyCallable_Check(callable)) {
@ -3714,6 +3716,15 @@ save_reduce(PicklerObject *self, PyObject *args, PyObject *obj)
return -1;
}
if (state_setter == Py_None)
state_setter = NULL;
else if (!PyCallable_Check(state_setter)) {
PyErr_Format(st->PicklingError, "sixth element of the tuple "
"returned by __reduce__ must be a function, not %s",
Py_TYPE(state_setter)->tp_name);
return -1;
}
if (self->proto >= 2) {
PyObject *name;
_Py_IDENTIFIER(__name__);
@ -3933,11 +3944,32 @@ save_reduce(PicklerObject *self, PyObject *args, PyObject *obj)
return -1;
if (state) {
if (save(self, state, 0) < 0 ||
_Pickler_Write(self, &build_op, 1) < 0)
return -1;
}
if (state_setter == NULL) {
if (save(self, state, 0) < 0 ||
_Pickler_Write(self, &build_op, 1) < 0)
return -1;
}
else {
/* If a state_setter is specified, call it instead of load_build to
* update obj's with its previous state.
* The first 4 save/write instructions push state_setter and its
* tuple of expected arguments (obj, state) onto the stack. The
* REDUCE opcode triggers the state_setter(obj, state) function
* call. Finally, because state-updating routines only do in-place
* modification, the whole operation has to be stack-transparent.
* Thus, we finally pop the call's output from the stack.*/
const char tupletwo_op = TUPLE2;
const char pop_op = POP;
if (save(self, state_setter, 0) < 0 ||
save(self, obj, 0) < 0 || save(self, state, 0) < 0 ||
_Pickler_Write(self, &tupletwo_op, 1) < 0 ||
_Pickler_Write(self, &reduce_op, 1) < 0 ||
_Pickler_Write(self, &pop_op, 1) < 0)
return -1;
}
}
return 0;
}