Issue #27934: Use float.__repr__ instead of plain repr when JSON-encoding an...

Issue #27934: Use float.__repr__ instead of plain repr when JSON-encoding an instance of a float subclass. Thanks Eddie James.

Lib/json/encoder.py

@@ -28,7 +28,7 @@ for i in range(0x20):
     #ESCAPE_DCT.setdefault(chr(i), '\\u%04x' % (i,))
 
 INFINITY = float('inf')
-FLOAT_REPR = repr
+FLOAT_REPR = float.__repr__
 
 def encode_basestring(s):
     """Return a JSON representation of a Python string

Lib/json/tests/test_float.py

@@ -32,6 +32,17 @@ class TestFloat(object):
                 self.assertNotEqual(res[0], res[0])
             self.assertRaises(ValueError, self.dumps, [val], allow_nan=False)
 
+    def test_float_subclasses_use_float_repr(self):
+        # Issue 27934.
+        class PeculiarFloat(float):
+            def __repr__(self):
+                return "I'm not valid JSON"
+            def __str__(self):
+                return "Neither am I"
+
+        val = PeculiarFloat(3.2)
+        self.assertEqual(self.loads(self.dumps(val)), val)
+
 
 class TestPyFloat(TestFloat, PyTest): pass
 class TestCFloat(TestFloat, CTest): pass

Misc/ACKS

@@ -636,6 +636,7 @@ Manuel Jacob
 David Jacobs
 Kevin Jacobs
 Kjetil Jacobsen
+Eddie James
 Bertrand Janin
 Geert Jansen
 Jack Jansen

Misc/NEWS

@@ -36,6 +36,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #27934: Use ``float.__repr__`` instead of plain ``repr`` when JSON-
+  encoding an instance of a float subclass. Thanks Eddie James.
+
 - Issue #27861: Fixed a crash in sqlite3.Connection.cursor() when a factory
   creates not a cursor.  Patch by Xiang Zhang.
 

Modules/_json.c

@@ -1960,8 +1960,8 @@ encoder_encode_float(PyEncoderObject *s, PyObject *obj)
             return PyString_FromString("NaN");
         }
     }
-    /* Use a better float format here? */
-    return PyObject_Repr(obj);
+    /* Make sure to use the base float class repr method */
+    return PyFloat_Type.tp_repr(obj);
 }
 
 static PyObject *