richcomparisons_py2.c

/* Helper to warn about deprecated tp_compare return values.  Return:
   -2 for an exception;
   -1 if v <  w;
    0 if v == w;
    1 if v  > w.
   (This function cannot return 2.)
*/
static int
adjust_tp_compare(int c)
{
    printf("adjust_tp_compare\n");
    if (PyErr_Occurred()) {
        if (c != -1 && c != -2) {
            PyObject *t, *v, *tb;
            PyErr_Fetch(&t, &v, &tb);
            if (PyErr_Warn(PyExc_RuntimeWarning,
                           "tp_compare didn't return -1 or -2 "
                           "for exception") < 0) {
                Py_XDECREF(t);
                Py_XDECREF(v);
                Py_XDECREF(tb);
            }
            else
                PyErr_Restore(t, v, tb);
        }
        return -2;
    }
    else if (c < -1 || c > 1) {
        if (PyErr_Warn(PyExc_RuntimeWarning,
                       "tp_compare didn't return -1, 0 or 1") < 0)
            return -2;
        else
            return c < -1 ? -1 : 1;
    }
    else {
        assert(c >= -1 && c <= 1);
        return c;
    }
}


/* Macro to get the tp_richcompare field of a type if defined */
#define RICHCOMPARE(t) (PyType_HasFeature((t), Py_TPFLAGS_HAVE_RICHCOMPARE) \
             ? (t)->tp_richcompare : NULL)

/* Try a genuine rich comparison, returning an object.  Return:
   NULL for exception;
   NotImplemented if this particular rich comparison is not implemented or
     undefined;
   some object not equal to NotImplemented if it is implemented
     (this latter object may not be a Boolean).
*/
static PyObject *
try_rich_compare(PyObject *v, PyObject *w, int op)
{
    printf("try_rich_compare\n");
    richcmpfunc f;
    PyObject *res;

    if (v->ob_type != w->ob_type &&
        PyType_IsSubtype(w->ob_type, v->ob_type) &&
        (f = RICHCOMPARE(w->ob_type)) != NULL) {
        printf("try_rich_compare - 1\n");
        res = (*f)(w, v, _Py_SwappedOp[op]);
        if (res != Py_NotImplemented)
            return res;
        Py_DECREF(res);
    }
    if ((f = RICHCOMPARE(v->ob_type)) != NULL) {
        printf("try_rich_compare - 2\n");
        res = (*f)(v, w, op);
        if (res != Py_NotImplemented)
            return res;
        Py_DECREF(res);
    }
    if ((f = RICHCOMPARE(w->ob_type)) != NULL) {
        printf("try_rich_compare - 3\n");
        return (*f)(w, v, _Py_SwappedOp[op]);
    }
    res = Py_NotImplemented;
    Py_INCREF(res);
    return res;
}

/* Try a genuine rich comparison, returning an int.  Return:
   -1 for exception (including the case where try_rich_compare() returns an
      object that's not a Boolean);
    0 if the outcome is false;
    1 if the outcome is true;
    2 if this particular rich comparison is not implemented or undefined.
*/
static int
try_rich_compare_bool(PyObject *v, PyObject *w, int op)
{
    printf("try_rich_compare_bool\n");
    PyObject *res;
    int ok;

    if (RICHCOMPARE(v->ob_type) == NULL && RICHCOMPARE(w->ob_type) == NULL)
        return 2; /* Shortcut, avoid INCREF+DECREF */
    res = try_rich_compare(v, w, op);
    if (res == NULL)
        return -1;
    if (res == Py_NotImplemented) {
        Py_DECREF(res);
        return 2;
    }
    ok = PyObject_IsTrue(res);
    Py_DECREF(res);
    return ok;
}

/* Try rich comparisons to determine a 3-way comparison.  Return:
   -2 for an exception;
   -1 if v  < w;
    0 if v == w;
    1 if v  > w;
    2 if this particular rich comparison is not implemented or undefined.
*/
static int
try_rich_to_3way_compare(PyObject *v, PyObject *w)
{
    printf("try_rich_to_3way_compare\n");
    static struct { int op; int outcome; } tries[3] = {
        /* Try this operator, and if it is true, use this outcome: */
        {Py_EQ, 0},
        {Py_LT, -1},
        {Py_GT, 1},
    };
    int i;

    if (RICHCOMPARE(v->ob_type) == NULL && RICHCOMPARE(w->ob_type) == NULL)
        return 2; /* Shortcut */

    for (i = 0; i < 3; i++) {
        switch (try_rich_compare_bool(v, w, tries[i].op)) {
        case -1:
            return -2;
        case 1:
            return tries[i].outcome;
        }
    }

    return 2;
}

/* Try a 3-way comparison, returning an int.  Return:
   -2 for an exception;
   -1 if v <  w;
    0 if v == w;
    1 if v  > w;
    2 if this particular 3-way comparison is not implemented or undefined.
*/
static int
try_3way_compare(PyObject *v, PyObject *w)
{
    printf("try_3way_compare\n");
    int c;
    cmpfunc f;

    /* Comparisons involving instances are given to instance_compare,
       which has the same return conventions as this function. */

    f = v->ob_type->tp_compare;
    if (PyInstance_Check(v))
        return (*f)(v, w);
    if (PyInstance_Check(w))
        return (*w->ob_type->tp_compare)(v, w);

    /* If both have the same (non-NULL) tp_compare, use it. */
    if (f != NULL && f == w->ob_type->tp_compare) {
        c = (*f)(v, w);
        return adjust_tp_compare(c);
    }

    /* If we're here, v and w,
        a) are not instances;
        b) have different types or a type without tp_compare; and
        c) don't have a user-defined tp_compare.
       tp_compare implementations in C assume that both arguments
       have their type, so we give up if the coercion fails or if
       it yields types which are still incompatible (which can
       happen with a user-defined nb_coerce).
    */
    c = PyNumber_CoerceEx(&v, &w);
    if (c < 0)
        return -2;
    if (c > 0)
        return 2;
    f = v->ob_type->tp_compare;
    if (f != NULL && f == w->ob_type->tp_compare) {
        c = (*f)(v, w);
        Py_DECREF(v);
        Py_DECREF(w);
        return adjust_tp_compare(c);
    }

    /* No comparison defined */
    Py_DECREF(v);
    Py_DECREF(w);
    return 2;
}

/* Final fallback 3-way comparison, returning an int.  Return:
   -2 if an error occurred;
   -1 if v <  w;
    0 if v == w;
    1 if v >  w.
*/
static int
default_3way_compare(PyObject *v, PyObject *w)
{
    printf("default_3way_compare\n");
    int c;
    const char *vname, *wname;

    if (v->ob_type == w->ob_type) {
        /* When comparing these pointers, they must be cast to
         * integer types (i.e. Py_uintptr_t, our spelling of C9X's
         * uintptr_t).  ANSI specifies that pointer compares other
         * than == and != to non-related structures are undefined.
         */
        Py_uintptr_t vv = (Py_uintptr_t)v;
        Py_uintptr_t ww = (Py_uintptr_t)w;
        return (vv < ww) ? -1 : (vv > ww) ? 1 : 0;
    }

    /* None is smaller than anything */
    if (v == Py_None)
        return -1;
    if (w == Py_None)
        return 1;

    /* different type: compare type names; numbers are smaller */
    if (PyNumber_Check(v))
        vname = "";
    else
        vname = v->ob_type->tp_name;
    if (PyNumber_Check(w))
        wname = "";
    else
        wname = w->ob_type->tp_name;
    c = strcmp(vname, wname);
    if (c < 0)
        return -1;
    if (c > 0)
        return 1;
    /* Same type name, or (more likely) incomparable numeric types */
    return ((Py_uintptr_t)(v->ob_type) < (
        Py_uintptr_t)(w->ob_type)) ? -1 : 1;
}

/* Do a 3-way comparison, by hook or by crook.  Return:
   -2 for an exception (but see below);
   -1 if v <  w;
    0 if v == w;
    1 if v >  w;
   BUT: if the object implements a tp_compare function, it returns
   whatever this function returns (whether with an exception or not).
*/
static int
do_cmp(PyObject *v, PyObject *w)
{
    printf("do_cmp\n");
    int c;
    cmpfunc f;

    if (v->ob_type == w->ob_type
        && (f = v->ob_type->tp_compare) != NULL) {
        c = (*f)(v, w);
        if (PyInstance_Check(v)) {
            /* Instance tp_compare has a different signature.
               But if it returns undefined we fall through. */
            if (c != 2)
                return c;
            /* Else fall through to try_rich_to_3way_compare() */
        }
        else
            return adjust_tp_compare(c);
    }
    /* We only get here if one of the following is true:
       a) v and w have different types
       b) v and w have the same type, which doesn't have tp_compare
       c) v and w are instances, and either __cmp__ is not defined or
          __cmp__ returns NotImplemented
    */
    c = try_rich_to_3way_compare(v, w);
    if (c < 2)
        return c;
    c = try_3way_compare(v, w);
    if (c < 2)
        return c;
    return default_3way_compare(v, w);
}

/* Return (new reference to) Py_True or Py_False. */
static PyObject *
convert_3way_to_object(int op, int c)
{
    printf("convert_3way_to_object\n");
    PyObject *result;
    switch (op) {
    case Py_LT: c = c <  0; break;
    case Py_LE: c = c <= 0; break;
    case Py_EQ: c = c == 0; break;
    case Py_NE: c = c != 0; break;
    case Py_GT: c = c >  0; break;
    case Py_GE: c = c >= 0; break;
    }
    result = c ? Py_True : Py_False;
    Py_INCREF(result);
    return result;
}

/* We want a rich comparison but don't have one.  Try a 3-way cmp instead.
   Return
   NULL      if error
   Py_True   if v op w
   Py_False  if not (v op w)
*/
static PyObject *
try_3way_to_rich_compare(PyObject *v, PyObject *w, int op)
{
    printf("try_3way_to_rich_compare\n");
    int c;

    c = try_3way_compare(v, w);
    if (c >= 2) {

        /* Py3K warning if types are not equal and comparison isn't == or !=  */
        if (Py_Py3kWarningFlag &&
            v->ob_type != w->ob_type && op != Py_EQ && op != Py_NE &&
            PyErr_WarnEx(PyExc_DeprecationWarning,
                       "comparing unequal types not supported "
                       "in 3.x", 1) < 0) {
            return NULL;
        }

        c = default_3way_compare(v, w);
    }
    if (c <= -2)
        return NULL;
    return convert_3way_to_object(op, c);
}

/* Do rich comparison on v and w.  Return
   NULL      if error
   Else a new reference to an object other than Py_NotImplemented, usually(?):
   Py_True   if v op w
   Py_False  if not (v op w)
*/
static PyObject *
do_richcmp(PyObject *v, PyObject *w, int op)
{
    printf("do_richcmp\n");
    PyObject *res;

    res = try_rich_compare(v, w, op);
    if (res != Py_NotImplemented)
        return res;
    Py_DECREF(res);

    return try_3way_to_rich_compare(v, w, op);
}

/* Return:
   NULL for exception;
   some object not equal to NotImplemented if it is implemented
     (this latter object may not be a Boolean).
*/
PyObject *
otherrichcompare(PyObject *v, PyObject *w, int op)
{
    printf("otherrichcompare\n");
    PyObject *res;

    assert(Py_LT <= op && op <= Py_GE);
    if (Py_EnterRecursiveCall(" in cmp"))
        return NULL;

    /* If the types are equal, and not old-style instances, try to
       get out cheap (don't bother with coercions etc.). */
    if (v->ob_type == w->ob_type && !PyInstance_Check(v)) {
        cmpfunc fcmp;
        richcmpfunc frich = RICHCOMPARE(v->ob_type);
        /* If the type has richcmp, try it first.  try_rich_compare
           tries it two-sided, which is not needed since we've a
           single type only. */
        if (frich != NULL) {
            printf("otherrichcompare - 1\n");
            res = (*frich)(v, w, op);
            if (res != Py_NotImplemented)
                goto Done;
            Py_DECREF(res);
        }
        /* No richcmp, or this particular richmp not implemented.
           Try 3-way cmp. */
        fcmp = v->ob_type->tp_compare;
        if (fcmp != NULL) {
            printf("otherrichcompare - 2\n");
            int c = (*fcmp)(v, w);
            c = adjust_tp_compare(c);
            if (c == -2) {
                res = NULL;
                goto Done;
            }
            res = convert_3way_to_object(op, c);
            goto Done;
        }
    }

    /* Fast path not taken, or couldn't deliver a useful result. */
    res = do_richcmp(v, w, op);
Done:
    Py_LeaveRecursiveCall();
    return res;
}

static PyObject *
myrichcmp(PyObject *m, PyObject *args)
{
    PyObject *op1, *op2;
    if (PyArg_UnpackTuple(args, "richcomp\n", 2, 2, &op1, &op2)) {
        return otherrichcompare(op1, op2, Py_EQ);
    } else {
        return NULL;
    }
}