Issue #8748: Fix two issues with comparisons between complex and integer

mdickinson · mdickinson · commit cc6a982de8b9 · 2010-05-21T14:55:26.000Z
objects.  (1) The comparison could incorrectly return True in some cases
(2**53+1 == complex(2**53) == 2**53), breaking transivity of equality.
(2) The comparison raised an OverflowError for large integers, leading
to unpredictable exceptions when combining integers and complex objects
in sets or dicts.

Patch by Meador Inge.
diff --git a/Lib/test/test_complex.py b/Lib/test/test_complex.py
@@ -110,12 +110,18 @@ def test_floordiv(self):
         self.assertRaises(TypeError, complex.__floordiv__, 3+0j, 0+0j)
 
     def test_richcompare(self):
-        self.assertRaises(OverflowError, complex.__eq__, 1+1j, 1<<10000)
+        self.assertIs(complex.__eq__(1+1j, 1<<10000), False)
         self.assertIs(complex.__lt__(1+1j, None), NotImplemented)
         self.assertIs(complex.__eq__(1+1j, 1+1j), True)
         self.assertIs(complex.__eq__(1+1j, 2+2j), False)
         self.assertIs(complex.__ne__(1+1j, 1+1j), False)
         self.assertIs(complex.__ne__(1+1j, 2+2j), True)
+        for i in range(1, 100):
+            f = i / 100.0
+            self.assertIs(complex.__eq__(f+0j, f), True)
+            self.assertIs(complex.__ne__(f+0j, f), False)
+            self.assertIs(complex.__eq__(complex(f, f), f), False)
+            self.assertIs(complex.__ne__(complex(f, f), f), True)
         self.assertIs(complex.__lt__(1+1j, 2+2j), NotImplemented)
         self.assertIs(complex.__le__(1+1j, 2+2j), NotImplemented)
         self.assertIs(complex.__gt__(1+1j, 2+2j), NotImplemented)
@@ -129,6 +135,23 @@ def test_richcompare(self):
         self.assertIs(operator.ne(1+1j, 1+1j), False)
         self.assertIs(operator.ne(1+1j, 2+2j), True)
 
+    def test_richcompare_boundaries(self):
+        def check(n, deltas, is_equal, imag = 0.0):
+            for delta in deltas:
+                i = n + delta
+                z = complex(i, imag)
+                self.assertIs(complex.__eq__(z, i), is_equal(delta))
+                self.assertIs(complex.__ne__(z, i), not is_equal(delta))
+        # For IEEE-754 doubles the following should hold:
+        #    x in [2 ** (52 + i), 2 ** (53 + i + 1)] -> x mod 2 ** i == 0
+        # where the interval is representable, of course.
+        for i in range(1, 10):
+            pow = 52 + i
+            mult = 2 ** i
+            check(2 ** pow, range(1, 101), lambda delta: delta % mult == 0)
+            check(2 ** pow, range(1, 101), lambda delta: False, float(i))
+        check(2 ** 53, range(-100, 0), lambda delta: True)
+
     def test_mod(self):
         # % is no longer supported on complex numbers
         self.assertRaises(TypeError, (1+1j).__mod__, 0+0j)
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -12,6 +12,19 @@ What's New in Python 3.2 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #8748: Fix two issues with comparisons between complex and integer
+  objects.  (1) The comparison could incorrectly return True in some cases
+  (2**53+1 == complex(2**53) == 2**53), breaking transivity of equality.
+  (2) The comparison raised an OverflowError for large integers, leading
+  to unpredictable exceptions when combining integers and complex objects
+  in sets or dicts.
+
+- Issue #8748: Fix comparisons between complex and integer objects.
+  These used to convert the integer object to a complex number before
+  doing the comparison, giving a potentially incorrect result when
+  that conversion involved precision loss.  (Ex: 2**53+1 ==
+  complex(2**53) returned True; now returns False.)
+
 - Issue #8766: Initialize _warnings module before importing the first module.
   Fix a crash if an empty directory called "encodings" exists in sys.path.
 
diff --git a/Objects/complexobject.c b/Objects/complexobject.c
@@ -620,22 +620,58 @@ static PyObject *
 complex_richcompare(PyObject *v, PyObject *w, int op)
 {
     PyObject *res;
-    Py_complex i, j;
-    TO_COMPLEX(v, i);
-    TO_COMPLEX(w, j);
+    Py_complex i;
+    int equal;
 
     if (op != Py_EQ && op != Py_NE) {
-        Py_INCREF(Py_NotImplemented);
-        return Py_NotImplemented;
+        goto Unimplemented;
     }
 
-    if ((i.real == j.real && i.imag == j.imag) == (op == Py_EQ))
-        res = Py_True;
+    assert(PyComplex_Check(v));
+    TO_COMPLEX(v, i);
+
+    if (PyLong_Check(w)) {
+        /* Check for 0.0 imaginary part first to avoid the rich
+         * comparison when possible.
+         */
+        if (i.imag == 0.0) {
+            PyObject *j, *sub_res;
+            j = PyFloat_FromDouble(i.real);
+            if (j == NULL)
+                return NULL;
+
+            sub_res = PyObject_RichCompare(j, w, op);
+            Py_DECREF(j);
+            return sub_res;
+        }
+        else {
+            equal = 0;
+        }
+    }
+    else if (PyFloat_Check(w)) {
+        equal = (i.real == PyFloat_AsDouble(w) && i.imag == 0.0);
+    }
+    else if (PyComplex_Check(w)) {
+        Py_complex j;
+
+        TO_COMPLEX(w, j);
+        equal = (i.real == j.real && i.imag == j.imag);
+    }
+    else {
+        goto Unimplemented;
+    }
+
+    if (equal == (op == Py_EQ))
+         res = Py_True;
     else
-        res = Py_False;
+         res = Py_False;
 
     Py_INCREF(res);
     return res;
+
+Unimplemented:
+    Py_INCREF(Py_NotImplemented);
+    return Py_NotImplemented;
 }
 
 static PyObject *
