Issue #27832: Make _normalize parameter to Fraction.__init__ keyword-only.

Lib/fractions.py

@@ -81,7 +81,7 @@ class Fraction(numbers.Rational):
     __slots__ = ('_numerator', '_denominator')
 
     # We're immutable, so use __new__ not __init__
-    def __new__(cls, numerator=0, denominator=None, _normalize=True):
+    def __new__(cls, numerator=0, denominator=None, *, _normalize=True):
         """Constructs a Rational.
 
         Takes a string like '3/2' or '1.5', another Rational instance, a

Lib/test/test_fractions.py

@@ -150,6 +150,7 @@ class FractionTest(unittest.TestCase):
         self.assertRaises(TypeError, F, "3/2", 3)
         self.assertRaises(TypeError, F, 3, 0j)
         self.assertRaises(TypeError, F, 3, 1j)
+        self.assertRaises(TypeError, F, 1, 2, 3)
 
     @requires_IEEE_754
     def testInitFromFloat(self):

Misc/NEWS

@@ -46,6 +46,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #27832: Make ``_normalize`` parameter to ``Fraction`` constuctor
+  keyword-only, so that ``Fraction(2, 3, 4)`` now raises ``TypeError``.
+
 - Issue #27539: Fix unnormalised ``Fraction.__pow__`` result in the case
   of negative exponent and negative base.