Issue 4998: restore utility of __slots__ on Fraction.

(forward merge of r68813).

Lib/numbers.py

@@ -15,6 +15,8 @@ class Number(metaclass=ABCMeta):
     If you just want to check if an argument x is a number, without
     caring what kind, use isinstance(x, Number).
     """
+    __slots__ = ()
+
     # Concrete numeric types must provide their own hash implementation
     __hash__ = None
 
@@ -38,6 +40,8 @@ class Complex(Number):
     type as described below.
     """
 
+    __slots__ = ()
+
     @abstractmethod
     def __complex__(self):
         """Return a builtin complex instance. Called for complex(self)."""
@@ -152,6 +156,8 @@ class Real(Complex):
     Real also provides defaults for the derived operations.
     """
 
+    __slots__ = ()
+
     @abstractmethod
     def __float__(self):
         """Any Real can be converted to a native float object.
@@ -264,6 +270,8 @@ Real.register(float)
 class Rational(Real):
     """.numerator and .denominator should be in lowest terms."""
 
+    __slots__ = ()
+
     @abstractproperty
     def numerator(self):
         raise NotImplementedError
@@ -287,6 +295,8 @@ class Rational(Real):
 class Integral(Rational):
     """Integral adds a conversion to int and the bit-string operations."""
 
+    __slots__ = ()
+
     @abstractmethod
     def __int__(self):
         """int(self)"""

Lib/test/test_fractions.py

@@ -407,6 +407,11 @@ class FractionTest(unittest.TestCase):
         self.assertEqual(id(r), id(copy(r)))
         self.assertEqual(id(r), id(deepcopy(r)))
 
+    def test_slots(self):
+        # Issue 4998
+        r = F(13, 7)
+        self.assertRaises(AttributeError, setattr, r, 'a', 10)
+
 def test_main():
     run_unittest(FractionTest, GcdTest)
 

Misc/NEWS

@@ -163,6 +163,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #4998: The memory saving effect of __slots__ had been lost on Fractions
+  which inherited from numbers.py which did not have __slots__ defined.  The
+  numbers hierarchy now has its own __slots__ declarations.
+
 - Issue #4631: Fix urlopen() result when an HTTP response uses chunked
   encoding.