Simplify choice()'s interaction with the private _randbelow() method (GH-19831)
diff --git a/Lib/random.py b/Lib/random.py
index 80fe447..8f840e1 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -265,10 +265,10 @@
return self.randrange(a, b+1)
def _randbelow_with_getrandbits(self, n):
- "Return a random int in the range [0,n). Raises ValueError if n==0."
+ "Return a random int in the range [0,n). Returns 0 if n==0."
if not n:
- raise ValueError("Boundary cannot be zero")
+ return 0
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
@@ -277,7 +277,7 @@
return r
def _randbelow_without_getrandbits(self, n, int=int, maxsize=1<<BPF):
- """Return a random int in the range [0,n). Raises ValueError if n==0.
+ """Return a random int in the range [0,n). Returns 0 if n==0.
The implementation does not use getrandbits, but only random.
"""
@@ -289,7 +289,7 @@
"To remove the range limitation, add a getrandbits() method.")
return int(random() * n)
if n == 0:
- raise ValueError("Boundary cannot be zero")
+ return 0
rem = maxsize % n
limit = (maxsize - rem) / maxsize # int(limit * maxsize) % n == 0
r = random()
@@ -303,11 +303,7 @@
def choice(self, seq):
"""Choose a random element from a non-empty sequence."""
- try:
- i = self._randbelow(len(seq))
- except ValueError:
- raise IndexError('Cannot choose from an empty sequence') from None
- return seq[i]
+ return seq[self._randbelow(len(seq))] # raises IndexError if seq is empty
def shuffle(self, x, random=None):
"""Shuffle list x in place, and return None.