diff -r 775b74e0e103 Include/code.h
--- a/Include/code.h	Wed Jan 20 12:16:21 2016 +0100
+++ b/Include/code.h	Wed Jan 20 14:59:07 2016 +0100
@@ -114,6 +114,12 @@ typedef struct _addr_pair {
 #ifndef Py_LIMITED_API
 PyAPI_FUNC(int) _PyCode_CheckLineNumber(PyCodeObject* co,
                                         int lasti, PyAddrPair *bounds);
+
+/* Create a comparable object used to compare constants taking in account the
+ * object type. For example, 0 (int) and 0.0 (float) must not be seen equal
+ * even if their value is equal. +0.0 and -0.0 are also considered as
+ * different. */
+PyAPI_FUNC(PyObject*) _PyCode_ConstantKey(PyObject *o);
 #endif
 
 PyAPI_FUNC(PyObject*) PyCode_Optimize(PyObject *code, PyObject* consts,
diff -r 775b74e0e103 Lib/test/test_compile.py
--- a/Lib/test/test_compile.py	Wed Jan 20 12:16:21 2016 +0100
+++ b/Lib/test/test_compile.py	Wed Jan 20 14:59:07 2016 +0100
@@ -572,6 +572,78 @@ if 1:
         exec(memoryview(b"ax = 123")[1:-1], namespace)
         self.assertEqual(namespace['x'], 12)
 
+    def check_constant(self, func, expected):
+        for const in func.__code__.co_consts:
+            if const != expected or type(const) != type(expected):
+                continue
+            if type(expected) in (tuple, frozenset):
+                if list(map(type, const)) != list(map(type, expected)):
+                    continue
+            # its ok, we found it
+            break
+        else:
+            self.fail("unable to find constant %r in %r"
+                      % (expected, func.__code__.co_consts))
+
+    # Merging equal constants is not a strict requirements for the Python
+    # semantics, it's a more an implementation detail.
+    @support.cpython_only
+    def test_merge_constants(self):
+        # Issue #25843: compile() must merge constants which are equal
+        # and have the same type.
+
+        def check_same_constant(const):
+            ns = {}
+            code = "f1, f2 = lambda: %r, lambda: %r" % (const, const)
+            exec(code, ns)
+            f1 = ns['f1']
+            f2 = ns['f2']
+            self.assertIs(f1.__code__, f2.__code__)
+            self.check_constant(f1, const)
+
+        check_same_constant(None)
+        check_same_constant(0)
+        check_same_constant(0.0)
+        check_same_constant(b'abc')
+        check_same_constant('abc')
+
+        # Note: "lambda: ..." emits "LOAD_CONST Ellipsis",
+        # whereas "lambda: Ellipsis" emits "LOAD_GLOBAL Ellipsis"
+        f1, f2 = lambda: ..., lambda: ...
+        self.assertIs(f1.__code__, f2.__code__)
+        self.check_constant(f1, Ellipsis)
+
+        # {0} is converted to a constant frozenset({0}) by the peephole
+        # optimizer
+        f1, f2 = lambda x: x in {0}, lambda x: x in {0}
+        self.assertIs(f1.__code__, f2.__code__)
+        self.check_constant(f1, frozenset({0}))
+
+    def test_dont_merge_constants(self):
+        # Issue #25843: compile() must not merge constants which are equal
+        # but have a different type.
+
+        def check_different_constants(const1, const2):
+            ns = {}
+            exec("f1, f2 = lambda: %r, lambda: %r" % (const1, const2), ns)
+            f1 = ns['f1']
+            f2 = ns['f2']
+            self.assertIsNot(f1.__code__, f2.__code__)
+            self.check_constant(f1, const1)
+            self.check_constant(f2, const2)
+
+        check_different_constants(0, 0.0)
+        check_different_constants(+0.0, -0.0)
+        check_different_constants(+0.0j, -0.0j)
+        check_different_constants((0,), (0.0,))
+
+        # {0} is converted to a constant frozenset({0}) by the peephole
+        # optimizer
+        f1, f2 = lambda x: x in {0}, lambda x: x in {0.0}
+        self.assertIsNot(f1.__code__, f2.__code__)
+        self.check_constant(f1, frozenset({0}))
+        self.check_constant(f2, frozenset({0.0}))
+
 
 class TestStackSize(unittest.TestCase):
     # These tests check that the computed stack size for a code object
diff -r 775b74e0e103 Objects/codeobject.c
--- a/Objects/codeobject.c	Wed Jan 20 12:16:21 2016 +0100
+++ b/Objects/codeobject.c	Wed Jan 20 14:59:07 2016 +0100
@@ -409,11 +409,130 @@ code_repr(PyCodeObject *co)
     }
 }
 
+PyObject*
+_PyCode_ConstantKey(PyObject *op)
+{
+    PyObject *key;
+
+    /* necessary to make sure types aren't coerced (e.g., float and complex)
+     * _and_ to distinguish 0.0 from -0.0 e.g. on IEEE platforms */
+    if (PyFloat_Check(op)) {
+        double d = PyFloat_AS_DOUBLE(op);
+        /* all we need is to make the tuple different in either the 0.0
+         * or -0.0 case from all others, just to avoid the "coercion".
+         */
+        if (d == 0.0 && copysign(1.0, d) < 0.0)
+            key = PyTuple_Pack(3, op, Py_TYPE(op), Py_None);
+        else
+            key = PyTuple_Pack(2, op, Py_TYPE(op));
+    }
+    else if (PyComplex_Check(op)) {
+        Py_complex z;
+        int real_negzero, imag_negzero;
+        /* For the complex case we must make complex(x, 0.)
+           different from complex(x, -0.) and complex(0., y)
+           different from complex(-0., y), for any x and y.
+           All four complex zeros must be distinguished.*/
+        z = PyComplex_AsCComplex(op);
+        real_negzero = z.real == 0.0 && copysign(1.0, z.real) < 0.0;
+        imag_negzero = z.imag == 0.0 && copysign(1.0, z.imag) < 0.0;
+        if (real_negzero && imag_negzero) {
+            key = PyTuple_Pack(5, op, Py_TYPE(op),
+                             Py_None, Py_None, Py_None);
+        }
+        else if (imag_negzero) {
+            key = PyTuple_Pack(4, op, Py_TYPE(op), Py_None, Py_None);
+        }
+        else if (real_negzero) {
+            key = PyTuple_Pack(3, op, Py_TYPE(op), Py_None);
+        }
+        else {
+            key = PyTuple_Pack(2, op, Py_TYPE(op));
+        }
+    }
+    else if (PyTuple_Check(op)) {
+        Py_ssize_t i, len;
+        PyObject *keys;
+
+        len = PyTuple_GET_SIZE(op);
+        keys = PyTuple_New(len);
+        if (keys == NULL)
+            return NULL;
+
+        for (i=0; i < len; i++) {
+            PyObject *item, *item_key;
+
+            item = PyTuple_GET_ITEM(op, i);
+            item_key = _PyCode_ConstantKey(item);
+            if (item_key == NULL) {
+                Py_DECREF(keys);
+                return NULL;
+            }
+
+            PyTuple_SET_ITEM(keys, i, item_key);
+        }
+
+        key = PyTuple_Pack(2, op, keys);
+    }
+    else if (PyAnySet_CheckExact(op)) {
+        Py_ssize_t pos = 0;
+        PyObject *item;
+        Py_hash_t hash;
+        Py_ssize_t i, len;
+        PyObject *keys;
+
+        len = PySet_GET_SIZE(op);
+        keys = PyTuple_New(len);
+        if (keys == NULL)
+            return NULL;
+
+        i = 0;
+        while (_PySet_NextEntry(op, &pos, &item, &hash)) {
+            PyObject *item_key;
+
+            item_key = _PyCode_ConstantKey(item);
+            if (item_key == NULL) {
+                Py_DECREF(keys);
+                return NULL;
+            }
+
+            PyTuple_SET_ITEM(keys, i, item_key);
+            i++;
+            if (i >= len) {
+                /* set size changed during iteration, ignore */
+                break;
+            }
+        }
+        return keys;
+    }
+    /* Py_None and Py_Ellipsis are singleton */
+    else if (op == Py_None || op == Py_Ellipsis
+             || PyLong_CheckExact(op)
+             || PyBool_Check(op)
+             || PyBytes_CheckExact(op)
+             || PyUnicode_CheckExact(op)
+                /* code_richcompare() uses _PyCode_ConstantKey() internally */
+             || PyCode_Check(op)) {
+        key = PyTuple_Pack(2, op, Py_TYPE(op));
+    }
+    else {
+        /* for other types, use the identifier to *not* merge them
+         * even if they are equal */
+        PyObject *obj_id = PyLong_FromVoidPtr(op);
+        if (obj_id == NULL)
+            return NULL;
+        key = PyTuple_Pack(3, op, Py_TYPE(op), obj_id);
+        Py_DECREF(obj_id);
+    }
+    return key;
+}
+
 static PyObject *
 code_richcompare(PyObject *self, PyObject *other, int op)
 {
     PyCodeObject *co, *cp;
     int eq;
+    PyObject *consts1, *consts2;
     PyObject *res;
 
     if ((op != Py_EQ && op != Py_NE) ||
@@ -439,8 +558,21 @@ code_richcompare(PyObject *self, PyObjec
     if (!eq) goto unequal;
     eq = PyObject_RichCompareBool(co->co_code, cp->co_code, Py_EQ);
     if (eq <= 0) goto unequal;
-    eq = PyObject_RichCompareBool(co->co_consts, cp->co_consts, Py_EQ);
+
+    /* compare constants */
+    consts1 = _PyCode_ConstantKey(co->co_consts);
+    if (!consts1)
+        return NULL;
+    consts2 = _PyCode_ConstantKey(cp->co_consts);
+    if (!consts2) {
+        Py_DECREF(consts1);
+        return NULL;
+    }
+    eq = PyObject_RichCompareBool(consts1, consts2, Py_EQ);
+    Py_DECREF(consts1);
+    Py_DECREF(consts2);
     if (eq <= 0) goto unequal;
+
     eq = PyObject_RichCompareBool(co->co_names, cp->co_names, Py_EQ);
     if (eq <= 0) goto unequal;
     eq = PyObject_RichCompareBool(co->co_varnames, cp->co_varnames, Py_EQ);
diff -r 775b74e0e103 Python/compile.c
--- a/Python/compile.c	Wed Jan 20 12:16:21 2016 +0100
+++ b/Python/compile.c	Wed Jan 20 14:59:07 2016 +0100
@@ -1105,47 +1105,8 @@ compiler_add_o(struct compiler *c, PyObj
 {
     PyObject *t, *v;
     Py_ssize_t arg;
-    double d;
-
-    /* necessary to make sure types aren't coerced (e.g., float and complex) */
-    /* _and_ to distinguish 0.0 from -0.0 e.g. on IEEE platforms */
-    if (PyFloat_Check(o)) {
-        d = PyFloat_AS_DOUBLE(o);
-        /* all we need is to make the tuple different in either the 0.0
-         * or -0.0 case from all others, just to avoid the "coercion".
-         */
-        if (d == 0.0 && copysign(1.0, d) < 0.0)
-            t = PyTuple_Pack(3, o, o->ob_type, Py_None);
-        else
-            t = PyTuple_Pack(2, o, o->ob_type);
-    }
-    else if (PyComplex_Check(o)) {
-        Py_complex z;
-        int real_negzero, imag_negzero;
-        /* For the complex case we must make complex(x, 0.)
-           different from complex(x, -0.) and complex(0., y)
-           different from complex(-0., y), for any x and y.
-           All four complex zeros must be distinguished.*/
-        z = PyComplex_AsCComplex(o);
-        real_negzero = z.real == 0.0 && copysign(1.0, z.real) < 0.0;
-        imag_negzero = z.imag == 0.0 && copysign(1.0, z.imag) < 0.0;
-        if (real_negzero && imag_negzero) {
-            t = PyTuple_Pack(5, o, o->ob_type,
-                             Py_None, Py_None, Py_None);
-        }
-        else if (imag_negzero) {
-            t = PyTuple_Pack(4, o, o->ob_type, Py_None, Py_None);
-        }
-        else if (real_negzero) {
-            t = PyTuple_Pack(3, o, o->ob_type, Py_None);
-        }
-        else {
-            t = PyTuple_Pack(2, o, o->ob_type);
-        }
-    }
-    else {
-        t = PyTuple_Pack(2, o, o->ob_type);
-    }
+
+    t = _PyCode_ConstantKey(o);
     if (t == NULL)
         return -1;