bpo-42772: Step argument ignored when stop is None. (GH-24018)
diff --git a/Lib/random.py b/Lib/random.py
index a4128c2..97495f0 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -96,6 +96,7 @@
SG_MAGICCONST = 1.0 + _log(4.5)
BPF = 53 # Number of bits in a float
RECIP_BPF = 2 ** -BPF
+_ONE = 1
class Random(_random.Random):
@@ -288,7 +289,7 @@ def randbytes(self, n):
## -------------------- integer methods -------------------
- def randrange(self, start, stop=None, step=1):
+ def randrange(self, start, stop=None, step=_ONE):
"""Choose a random item from range(start, stop[, step]).
This fixes the problem with randint() which includes the
@@ -311,7 +312,12 @@ def randrange(self, start, stop=None, step=1):
_warn('randrange() will raise TypeError in the future',
DeprecationWarning, 2)
raise ValueError("non-integer arg 1 for randrange()")
+
if stop is None:
+ # We don't check for "step != 1" because it hasn't been
+ # type checked and converted to an integer yet.
+ if step is not _ONE:
+ raise TypeError('Missing a non-None stop argument')
if istart > 0:
return self._randbelow(istart)
raise ValueError("empty range for randrange()")
diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py
index 436f3c9..41a26e3 100644
--- a/Lib/test/test_random.py
+++ b/Lib/test/test_random.py
@@ -562,6 +562,14 @@ def test_randrange_argument_handling(self):
with self.assertRaises(ValueError):
randrange(10, 20, 1.5)
+ def test_randrange_step(self):
+ # bpo-42772: When stop is None, the step argument was being ignored.
+ randrange = self.gen.randrange
+ with self.assertRaises(TypeError):
+ randrange(1000, step=100)
+ with self.assertRaises(TypeError):
+ randrange(1000, None, step=100)
+
def test_randbelow_logic(self, _log=log, int=int):
# check bitcount transition points: 2**i and 2**(i+1)-1
# show that: k = int(1.001 + _log(n, 2))
diff --git a/Misc/NEWS.d/next/Library/2020-12-30-17-16-43.bpo-42772.Xe7WFV.rst b/Misc/NEWS.d/next/Library/2020-12-30-17-16-43.bpo-42772.Xe7WFV.rst
new file mode 100644
index 0000000..7f4ae7a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-12-30-17-16-43.bpo-42772.Xe7WFV.rst
@@ -0,0 +1,2 @@
+randrange() now raises a TypeError when step is specified without a stop
+argument. Formerly, it silently ignored the step argument.