minor styling changes and more explicit test for generators

fn/iters.py

@@ -107,8 +107,7 @@ def group_by(keyfunc, iterable):
     """
     grouped = {}
     for item in iterable:
-        key = keyfunc(item)
-        grouped.setdefault(key, []).append(item)
+        grouped.setdefault(keyfunc(item), []).append(item)
     return grouped
 
 def roundrobin(*iterables):

tests.py

@@ -491,10 +491,18 @@ def test_grouper(self):
         self.assertEqual(["G","x","x"], list(c))
 
     def test_group_by(self):
-        iterable = (s for s in ['1', '12', 'a', '123', 'ab'])
-        grouped = iters.group_by(lambda s: len(s), iterable)
+        # verify grouping logic
+        grouped = iters.group_by(len, ['1', '12', 'a', '123', 'ab'])
         self.assertEqual({1: ['1', 'a'], 2: ['12', 'ab'], 3: ['123']}, grouped)
 
+        # verify it works with any iterable - not only lists
+        def gen():
+            yield '1'
+            yield '12'
+
+        grouped = iters.group_by(len, gen())
+        self.assertEqual({1: ['1'], 2: ['12']}, grouped)
+
     def test_roundrobin(self):
         r = iters.roundrobin('ABC', 'D', 'EF')
         self.assertEqual(["A","D","E","B","F","C"], list(r))