bpo-29894: Deprecate returning an instance of complex subclass from __complex__....

In a future versions of Python this can be an error.

diff --git a/Lib/test/test_complex.py b/Lib/test/test_complex.py
index cee49343e268a23c76f37c305d398eb29be423fb..2d883c5348ea6fa8d4ef50391b4cf2779dad7d90 100644 (file)
--- a/Lib/test/test_complex.py
+++ b/Lib/test/test_complex.py
@@ -383,8 +383,9 @@ class ComplexTest(unittest.TestCase):
             def __complex__(self):
                 return None
 
-        self.assertAlmostEqual(complex(complex0(1j)), 42j)
-        self.assertAlmostEqual(complex(complex1(1j)), 2j)
+        self.assertEqual(complex(complex0(1j)), 42j)
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(complex(complex1(1j)), 2j)
         self.assertRaises(TypeError, complex, complex2(1j))
 
     @support.requires_IEEE_754

diff --git a/Lib/test/test_getargs2.py b/Lib/test/test_getargs2.py
index 8a194aa03d42784685d674e2e8b3153bcdb8ac0a..e5d9aa64ee2dfd1160731541f336d4a5bccb2508 100644 (file)
--- a/Lib/test/test_getargs2.py
+++ b/Lib/test/test_getargs2.py
@@ -408,7 +408,8 @@ class Float_TestCase(unittest.TestCase):
         self.assertEqual(getargs_D(ComplexSubclass(7.5+0.25j)), 7.5+0.25j)
         self.assertEqual(getargs_D(ComplexSubclass2(7.5+0.25j)), 7.5+0.25j)
         self.assertRaises(TypeError, getargs_D, BadComplex())
-        self.assertEqual(getargs_D(BadComplex2()), 4.25+0.5j)
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(getargs_D(BadComplex2()), 4.25+0.5j)
         self.assertEqual(getargs_D(BadComplex3(7.5+0.25j)), 7.5+0.25j)
 
         for x in (DBL_MIN, -DBL_MIN, DBL_MAX, -DBL_MAX, INF, -INF):

diff --git a/Misc/NEWS b/Misc/NEWS
index 9b0414a8e57b448bfb13c13271d50810aa0e674d..a5653c8524ff4e2e6bf9e062f15dfc7df840bbd8 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,10 @@ What's New in Python 3.7.0 alpha 1?
 Core and Builtins
 -----------------
 
+- bpo-29894: The deprecation warning is emitted if __complex__ returns an
+  instance of a strict subclass of complex.  In a future versions of Python
+  this can be an error.
+
 - bpo-29859: Show correct error messages when any of the pthread_* calls in
   thread_pthread.h fails.
 

diff --git a/Objects/complexobject.c b/Objects/complexobject.c
index 773ddb3d7aebb47875810301dd2f1d97cceda89b..5ebb50435e7401119a1e4de42b6f08b81acedb60 100644 (file)
--- a/Objects/complexobject.c
+++ b/Objects/complexobject.c
@@ -274,7 +274,8 @@ PyComplex_ImagAsDouble(PyObject *op)
 }
 
 static PyObject *
-try_complex_special_method(PyObject *op) {
+try_complex_special_method(PyObject *op)
+{
     PyObject *f;
     _Py_IDENTIFIER(__complex__);
 
@@ -282,9 +283,22 @@ try_complex_special_method(PyObject *op) {
     if (f) {
         PyObject *res = _PyObject_CallNoArg(f);
         Py_DECREF(f);
-        if (res != NULL && !PyComplex_Check(res)) {
-            PyErr_SetString(PyExc_TypeError,
-                "__complex__ should return a complex object");
+        if (!res || PyComplex_CheckExact(res)) {
+            return res;
+        }
+        if (!PyComplex_Check(res)) {
+            PyErr_Format(PyExc_TypeError,
+                "__complex__ returned non-complex (type %.200s)",
+                res->ob_type->tp_name);
+            Py_DECREF(res);
+            return NULL;
+        }
+        /* Issue #29894: warn if 'res' not of exact type complex. */
+        if (PyErr_WarnFormat(PyExc_DeprecationWarning, 1,
+                "__complex__ returned non-complex (type %.200s).  "
+                "The ability to return an instance of a strict subclass of complex "
+                "is deprecated, and may be removed in a future version of Python.",
+                res->ob_type->tp_name)) {
             Py_DECREF(res);
             return NULL;
         }
@@ -1030,12 +1044,7 @@ complex_new_impl(PyTypeObject *type, PyObject *r, PyObject *i)
         }
         if (tmp == NULL)
             return NULL;
-        if (!PyFloat_Check(tmp)) {
-            PyErr_SetString(PyExc_TypeError,
-                            "float(r) didn't return a float");
-            Py_DECREF(tmp);
-            return NULL;
-        }
+        assert(PyFloat_Check(tmp));
         cr.real = PyFloat_AsDouble(tmp);
         cr.imag = 0.0;
         Py_DECREF(tmp);