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Another crack at bug #1460340: make random.sample(dict)

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work, this time by ugly brute force.
This commit is contained in:
Tim Peters 2006-04-01 00:26:53 +00:00
parent 2a9a6b0e86
commit c17976e983
3 changed files with 37 additions and 5 deletions
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17
Lib/random.py
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@ -285,6 +285,15 @@ class Random(_random.Random):
large population: sample(xrange(10000000), 60)
"""
# XXX Although the documentation says `population` is "a sequence",
# XXX attempts are made to cater to any iterable with a __len__
# XXX method. This has had mixed success. Examples from both
# XXX sides: sets work fine, and should become officially supported;
# XXX dicts are much harder, and have failed in various subtle
# XXX ways across attempts. Support for mapping types should probably
# XXX be dropped (and users should pass mapping.keys() or .values()
# XXX explicitly).
# Sampling without replacement entails tracking either potential
# selections (the pool) in a list or previous selections in a set.
@ -304,7 +313,9 @@ class Random(_random.Random):
setsize = 21 # size of a small set minus size of an empty list
if k > 5:
setsize += 4 ** _ceil(_log(k * 3, 4)) # table size for big sets
if n <= setsize: # is an n-length list smaller than a k-length set
if n <= setsize or hasattr(population, "keys"):
# An n-length list is smaller than a k-length set, or this is a
# mapping type so the other algorithm wouldn't work.
pool = list(population)
for i in xrange(k): # invariant: non-selected at [0,n-i)
j = _int(random() * (n-i))
@ -320,10 +331,10 @@ class Random(_random.Random):
j = _int(random() * n)
selected_add(j)
result[i] = population[j]
except (TypeError, KeyError): # handle sets and dictionaries
except (TypeError, KeyError): # handle (at least) sets
if isinstance(population, list):
raise
return self.sample(list(population), k)
return self.sample(tuple(population), k)
return result
## -------------------- real-valued distributions -------------------