make itertools.chain be a class and from_iterable a classmethod of chain

lib/itertools.py

@@ -17,10 +17,20 @@
 import _collections
 import sys
 
-def chain(*iterables):
-  for it in iterables:
-    for element in it:
-      yield element
+class chain(object):
+
+    def from_iterable(cls, iterable):
+        return cls(*iterable)
+
+    from_iterable = classmethod(from_iterable)
+
+    def __init__(self, *iterables):
+        self.iterables = iterables
+
+    def __iter__(self):
+        for it in self.iterables:
+            for element in it:
+                yield element
 
 def compress(data, selectors):
   return (d for d,s in izip(data, selectors) if s)
@@ -49,11 +59,6 @@ def dropwhile(predicate, iterable):
   for x in iterable:
     yield x
 
-def from_iterable(iterables):
-  for it in iterables:
-    for element in it:
-      yield element
-
 def ifilter(predicate, iterable):
   if predicate is None:
     predicate = bool

lib/itertools_test.py

@@ -46,6 +46,17 @@ def TestDropwhile():
     got = tuple(itertools.dropwhile(*args))
     assert got == want, 'tuple(dropwhile%s) == %s, want %s' % (args, got, want)
 
+def TestChain():
+  r = range(10)
+  cases = [
+    ([r], tuple(r)),
+    ([r, r], tuple(r) + tuple(r)),
+    ([], ())
+  ]
+  for args, want in cases:
+    got = tuple(itertools.chain(*args))
+    assert got == want, 'tuple(chain%s) == %s, want %s' % (args, got, want)
+
 def TestFromIterable():
   r = range(10)
   cases = [
@@ -54,7 +65,7 @@ def TestFromIterable():
     ([], ())
   ]
   for args, want in cases:
-    got = tuple(itertools.from_iterable(args))
+    got = tuple(itertools.chain.from_iterable(args))
     assert got == want, 'tuple(from_iterable%s) == %s, want %s' % (args, got, want)
 
 def TestIFilter():