[Python-checkins] bpo-33203: Ensure random.choice always raises IndexError on empty sequence (GH-6338) (GH-6387)
Raymond Hettinger
webhook-mailer at python.org
Thu Apr 5 12:02:15 EDT 2018
https://github.com/python/cpython/commit/baf304e82e1b54dbeee6b78ddf168e33ed8d557a
commit: baf304e82e1b54dbeee6b78ddf168e33ed8d557a
branch: 3.7
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: Raymond Hettinger <rhettinger at users.noreply.github.com>
date: 2018-04-05T09:02:12-07:00
summary:
bpo-33203: Ensure random.choice always raises IndexError on empty sequence (GH-6338) (GH-6387)
(cherry picked from commit 091e95e9004b794280ab35becec2c3e30dd5e96e)
Co-authored-by: Wolfgang Maier <wolfgang.maier at biologie.uni-freiburg.de>
files:
A Misc/NEWS.d/next/Library/2018-04-05-11-09-45.bpo-33203.Hje9Py.rst
M Lib/random.py
M Lib/test/test_random.py
diff --git a/Lib/random.py b/Lib/random.py
index 91065b7e3037..0bc24174e13f 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -242,6 +242,8 @@ def _randbelow(self, n, int=int, maxsize=1<<BPF, type=type,
"enough bits to choose from a population range this large.\n"
"To remove the range limitation, add a getrandbits() method.")
return int(random() * n)
+ if n == 0:
+ raise ValueError("Boundary cannot be zero")
rem = maxsize % n
limit = (maxsize - rem) / maxsize # int(limit * maxsize) % n == 0
r = random()
diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py
index 468c4a467e5d..eee245df48a1 100644
--- a/Lib/test/test_random.py
+++ b/Lib/test/test_random.py
@@ -651,7 +651,10 @@ def test_randbelow_overridden_random(self, random_mock):
# Population range too large (n >= maxsize)
self.gen._randbelow(maxsize+1, maxsize = maxsize)
self.gen._randbelow(5640, maxsize = maxsize)
-
+ # issue 33203: test that _randbelow raises ValueError on
+ # n == 0 also in its getrandbits-independent branch.
+ with self.assertRaises(ValueError):
+ self.gen._randbelow(0, maxsize=maxsize)
# This might be going too far to test a single line, but because of our
# noble aim of achieving 100% test coverage we need to write a case in
# which the following line in Random._randbelow() gets executed:
diff --git a/Misc/NEWS.d/next/Library/2018-04-05-11-09-45.bpo-33203.Hje9Py.rst b/Misc/NEWS.d/next/Library/2018-04-05-11-09-45.bpo-33203.Hje9Py.rst
new file mode 100644
index 000000000000..ab6d17b5d1ba
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-04-05-11-09-45.bpo-33203.Hje9Py.rst
@@ -0,0 +1,3 @@
+``random.Random.choice()`` now raises ``IndexError`` for empty sequences
+consistently even when called from subclasses without a ``getrandbits()``
+implementation.
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