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Fix corner case for Random.choice() and add tests.

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This commit is contained in:
Raymond Hettinger 2010-09-07 10:06:56 +00:00
parent c324697bac
commit dc4872eefe
2 changed files with 12 additions and 1 deletions
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6
Lib/random.py
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@ -239,7 +239,11 @@ class Random(_random.Random):
def choice(self, seq): def choice(self, seq):
"""Choose a random element from a non-empty sequence.""" """Choose a random element from a non-empty sequence."""
return seq[self._randbelow(len(seq))] # raises IndexError if seq is empty try:
i = self._randbelow(len(seq))
except ValueError:
raise IndexError('Cannot choose from an empty sequence')
return seq[i]
def shuffle(self, x, random=None, int=int): def shuffle(self, x, random=None, int=int):
"""x, random=random.random -> shuffle list x in place; return None. """x, random=random.random -> shuffle list x in place; return None.

7
Lib/test/test_random.py
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@ -42,6 +42,13 @@ class TestBasicOps(unittest.TestCase):
self.assertRaises(TypeError, self.gen.seed, 1, 2, 3, 4) self.assertRaises(TypeError, self.gen.seed, 1, 2, 3, 4)
self.assertRaises(TypeError, type(self.gen), []) self.assertRaises(TypeError, type(self.gen), [])
def test_choice(self):
choice = self.gen.choice
with self.assertRaises(IndexError):
choice([])
self.assertEqual(choice([50]), 50)
self.assertIn(choice([25, 75]), [25, 75])
def test_sample(self): def test_sample(self):
# For the entire allowable range of 0 <= k <= N, validate that # For the entire allowable range of 0 <= k <= N, validate that
# the sample is of the correct length and contains only unique items # the sample is of the correct length and contains only unique items