bpo-37319: Deprecated support of non-integer arguments in random.randrange().

Doc/library/random.rst

@@ -130,6 +130,10 @@ Functions for integers
       values.  Formerly it used a style like ``int(random()*n)`` which could produce
       slightly uneven distributions.
 
+   .. deprecated:: 3.9
+      Accepting non-integer arguments is deprecated.
+
+
 .. function:: randint(a, b)
 
    Return a random integer *N* such that ``a <= N <= b``.  Alias for

Doc/whatsnew/3.9.rst

@@ -612,6 +612,9 @@ Deprecated
   by :c:func:`Py_Initialize()` since Python 3.7.
   (Contributed by Victor Stinner in :issue:`39877`.)
 
+* Deprecated support of non-integer arguments in :func:`random.randrange`.
+  (Contributed by Serhiy Storchaka in :issue:`37319`.)
+
 
 Removed
 =======

Lib/random.py

@@ -44,6 +44,7 @@
 from _collections_abc import Set as _Set, Sequence as _Sequence
 from itertools import accumulate as _accumulate, repeat as _repeat
 from bisect import bisect as _bisect
+from operator import index as _index
 import os as _os
 
 try:
@@ -67,7 +68,7 @@
 SG_MAGICCONST = 1.0 + _log(4.5)
 BPF = 53        # Number of bits in a float
 RECIP_BPF = 2**-BPF
-
+_ONE = 1
 
 # Translated by Guido van Rossum from C source provided by
 # Adrian Baddeley.  Adapted by Raymond Hettinger for use with
@@ -208,7 +209,7 @@ def __reduce__(self):
 
 ## -------------------- integer methods  -------------------
 
-    def randrange(self, start, stop=None, step=1, _int=int):
+    def randrange(self, start, stop=None, step=_ONE, _index=_index, _int=int):
         """Choose a random item from range(start, stop[, step]).
 
         This fixes the problem with randint() which includes the
@@ -218,28 +219,44 @@ def randrange(self, start, stop=None, step=1, _int=int):
 
         # This code is a bit messy to make it fast for the
         # common case while still doing adequate error checking.
-        istart = _int(start)
-        if istart != start:
-            raise ValueError("non-integer arg 1 for randrange()")
+        try:
+            istart = _index(start)
+        except TypeError:
+            istart = _int(start)
+            if istart != start:
+                raise ValueError("non-integer arg 1 for randrange()")
+            _warn('non-integer arg 1 for randrange()',
+                  DeprecationWarning, 2)
         if stop is None:
             if istart > 0:
                 return self._randbelow(istart)
             raise ValueError("empty range for randrange()")
 
         # stop argument supplied.
-        istop = _int(stop)
-        if istop != stop:
-            raise ValueError("non-integer stop for randrange()")
+        try:
+            istop = _index(stop)
+        except TypeError:
+            istop = _int(stop)
+            if istop != stop:
+                raise ValueError("non-integer stop for randrange()")
+            _warn('non-integer stop for randrange()',
+                  DeprecationWarning, 2)
         width = istop - istart
-        if step == 1 and width > 0:
-            return istart + self._randbelow(width)
-        if step == 1:
+        # Fast path.
+        if step is _ONE:
+            if width > 0:
+                return istart + self._randbelow(width)
             raise ValueError("empty range for randrange() (%d, %d, %d)" % (istart, istop, width))
 
         # Non-unit step argument supplied.
-        istep = _int(step)
-        if istep != step:
-            raise ValueError("non-integer step for randrange()")
+        try:
+            istep = _index(step)
+        except TypeError:
+            istep = _int(step)
+            if istep != step:
+                raise ValueError("non-integer step for randrange()")
+            _warn('non-integer step for randrange()',
+                  DeprecationWarning, 2)
         if istep > 0:
             n = (width + istep - 1) // istep
         elif istep < 0:

Lib/test/test_random.py

@@ -367,12 +367,22 @@ def test_randrange_errors(self):
         raises(3, 3)
         raises(-721)
         raises(0, 100, -12)
+        self.assertWarns(DeprecationWarning, raises, 3, 3, 1.0)
         # Non-integer start/stop
         raises(3.14159)
+        self.assertWarns(DeprecationWarning, self.gen.randrange, 3.0)
+        self.assertWarns(DeprecationWarning, self.gen.randrange, Fraction(3, 1))
+        raises('3')
         raises(0, 2.71828)
+        self.assertWarns(DeprecationWarning, self.gen.randrange, 0, 2.0)
+        self.assertWarns(DeprecationWarning, self.gen.randrange, 0, Fraction(2, 1))
+        raises(0, '2')
         # Zero and non-integer step
         raises(0, 42, 0)
         raises(0, 42, 3.14159)
+        self.assertWarns(DeprecationWarning, self.gen.randrange, 0, 42, 3.0)
+        self.assertWarns(DeprecationWarning, self.gen.randrange, 0, 42, Fraction(3, 1))
+        raises(0, 42, '3')
 
     def test_genrandbits(self):
         # Verify ranges

Misc/NEWS.d/next/Library/2020-03-22-21-33-31.bpo-37319.BrIAir.rst

@@ -0,0 +1 @@
+Deprecated support of non-integer arguments in :func:`random.randrange`.