Added a "generate k-combinations of a list" example posted to c.l.py.
diff --git a/Lib/test/test_generators.py b/Lib/test/test_generators.py
index 8a82407..82ab01c 100644
--- a/Lib/test/test_generators.py
+++ b/Lib/test/test_generators.py
@@ -281,7 +281,7 @@
"""
-# A few examples from Iterator-List and Python-Dev email.
+# Examples from Iterator-List and Python-Dev and c.l.py.
email_tests = """
@@ -319,6 +319,54 @@
...
File "<string>", line 2, in g
ValueError: generator already executing
+
+Next one was posted to c.l.py.
+
+>>> def gcomb(x, k):
+... "Generate all combinations of k elements from list x."
+...
+... if k > len(x):
+... return
+... if k == 0:
+... yield []
+... else:
+... first, rest = x[0], x[1:]
+... # A combination does or doesn't contain first.
+... # If it does, the remainder is a k-1 comb of rest.
+... for c in gcomb(rest, k-1):
+... c.insert(0, first)
+... yield c
+... # If it doesn't contain first, it's a k comb of rest.
+... for c in gcomb(rest, k):
+... yield c
+
+>>> seq = range(1, 5)
+>>> for k in range(len(seq) + 2):
+... print "%d-combs of %s:" % (k, seq)
+... for c in gcomb(seq, k):
+... print " ", c
+0-combs of [1, 2, 3, 4]:
+ []
+1-combs of [1, 2, 3, 4]:
+ [1]
+ [2]
+ [3]
+ [4]
+2-combs of [1, 2, 3, 4]:
+ [1, 2]
+ [1, 3]
+ [1, 4]
+ [2, 3]
+ [2, 4]
+ [3, 4]
+3-combs of [1, 2, 3, 4]:
+ [1, 2, 3]
+ [1, 2, 4]
+ [1, 3, 4]
+ [2, 3, 4]
+4-combs of [1, 2, 3, 4]:
+ [1, 2, 3, 4]
+5-combs of [1, 2, 3, 4]:
"""
# Fun tests (for sufficiently warped notions of "fun").