-

cool-RR · cool-RR · commit 71465836ac07 · 2013-08-17T02:32:54.000+03:00
diff --git a/python_toolbox/cute_iter_tools.py b/python_toolbox/cute_iter_tools.py
@@ -7,6 +7,7 @@
 
 from __future__ import with_statement
 
+import collections
 import itertools
 import __builtin__
 
@@ -199,4 +200,40 @@ def get_items(iterable, n):
     If there are less than `n` items, no exception will be raised. Whatever
     items are there will be returned.
     '''
-    return tuple(shorten(iterable, n))
+    return tuple(shorten(iterable, n))
+
+
+def double_filter(filter_function, iterable):
+    iterator = iter(iterable)
+    
+    true_deque = collections.deque()
+    false_deque = collections.deque()
+    
+    def process_value():
+        value = next(iterator)
+        if filter_function(value):
+            true_deque.append(value)
+        else:
+            false_deque.append(value)
+    
+    def make_true_iterator():
+        while True:
+            try:
+                yield true_deque.popleft()
+            except IndexError:
+                try:
+                    process_value()
+                except StopIteration:
+                    break
+
+    def make_false_iterator():
+        while True:
+            try:
+                yield false_deque.popleft()
+            except IndexError:
+                try:
+                    process_value()
+                except StopIteration:
+                    break
+                
+    return (make_true_iterator(), make_false_iterator())
diff --git a/test_python_toolbox/test_cute_iter_tools/test_double_filter.py b/test_python_toolbox/test_cute_iter_tools/test_double_filter.py
@@ -0,0 +1,18 @@
+# Copyright 2009-2013 Ram Rachum.
+# This program is distributed under the MIT license.
+
+from python_toolbox.cute_iter_tools import double_filter
+
+
+def test_double_filter():
+    
+    (first_iterable, second_iterable) = \
+                        double_filter(lambda value: value % 2 == 0, xrange(20))
+    assert tuple(first_iterable) == tuple(xrange(0, 20, 2))
+    assert tuple(second_iterable) == tuple(xrange(1, 20, 2))
+    
+    (first_iterable, second_iterable) = \
+                        double_filter(lambda value: value % 3 == 0, xrange(20))
+    assert tuple(first_iterable) == tuple(xrange(0, 20, 3))
+    assert tuple(second_iterable) == tuple(i for i in xrange(20) if i % 3 != 0)
+    
