Another crack at bug #1460340: make random.sample(dict)
work, this time by ugly brute force.
diff --git a/Lib/random.py b/Lib/random.py
index 943fa51..465f477 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -285,6 +285,15 @@
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 @@
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 @@
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 -------------------