Implementation for fixing issue #124

functional/test/test_functional.py

@@ -645,6 +645,11 @@ def test_partition(self):
         self.assert_type(p1)
         self.assert_type(p2)
 
+        result = self.seq([[1, 2, 3], [4, 5, 6]]).flatten().partition(lambda x: x > 2)
+        expect = [[3, 4, 5, 6], [1, 2]]
+        self.assertIteratorEqual(expect, list(result))
+        self.assert_type(result)
+
     def test_cartesian(self):
         result = seq.range(3).cartesian(range(3)).list()
         self.assertListEqual(result, list(product(range(3), range(3))))

functional/transformations.py

@@ -659,6 +659,18 @@ def sliding_t(wrap, size, step):
     )
 
 
+def partition_impl(wrap, predicate, sequence):
+    truthy_partition = []
+    falsy_partition = []
+    for e in sequence:
+        if predicate(e):
+            truthy_partition.append(e)
+        else:
+            falsy_partition.append(e)
+
+    return wrap((wrap(truthy_partition), wrap(falsy_partition)))
+
+
 def partition_t(wrap, func):
     """
     Transformation for Sequence.partition
@@ -668,9 +680,7 @@ def partition_t(wrap, func):
     """
     return Transformation(
         'partition({0})'.format(name(func)),
-        lambda sequence: wrap(
-            (wrap(filter(func, sequence)), wrap(filter(lambda val: not func(val), sequence)))
-        ),
+        partial(partition_impl, wrap, func),
         None
     )