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bpo-40282: Allow random.getrandbits(0) (GH-19539)

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Antoine Pitrou 2020-04-17 19:32:14 +02:00 • committed by GitHub
parent d7c657d4b1
commit 75a3378810
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5 changed files with 42 additions and 44 deletions
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6
Lib/random.py
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@ -261,6 +261,8 @@ class Random(_random.Random):
def _randbelow_with_getrandbits(self, n):
"Return a random int in the range [0,n). Raises ValueError if n==0."
if not n:
raise ValueError("Boundary cannot be zero")
getrandbits = self.getrandbits
k = n.bit_length() # don't use (n-1) here because n can be 1
r = getrandbits(k) # 0 <= r < 2**k
@ -733,8 +735,8 @@ class SystemRandom(Random):
def getrandbits(self, k):
"""getrandbits(k) -> x. Generates an int with k random bits."""
if k <= 0:
raise ValueError('number of bits must be greater than zero')
if k < 0:
raise ValueError('number of bits must be non-negative')
numbytes = (k + 7) // 8 # bits / 8 and rounded up
x = int.from_bytes(_urandom(numbytes), 'big')
return x >> (numbytes * 8 - k) # trim excess bits