support iterators in view.map

Some objects are not sliceable (e.g. xrange). For these, fall back
on itertools.islice.

tests included

reported on IRC by @juliantaylor

IPython/parallel/client/map.py

@@ -27,6 +27,7 @@
 from __future__ import division
 
 import types
+from itertools import islice
 
 from IPython.utils.data import flatten as utils_flatten
 
@@ -77,9 +78,14 @@ def getPartition(self, seq, p, q):
             else:
                 lo.append(n*basesize + remainder)
                 hi.append(lo[-1] + basesize)
-
 
-        result = seq[lo[p]:hi[p]]
+        try:
+            result = seq[lo[p]:hi[p]]
+        except TypeError:
+            # some objects (iterators) can't be sliced,
+            # use islice:
+            result = list(islice(seq, lo[p], hi[p]))
+
         return result
 
     def joinPartitions(self, listOfPartitions):

IPython/parallel/tests/test_lbview.py

@@ -95,6 +95,17 @@ def slow_f(x):
         # Ensure that results came in order
         self.assertEquals(astheycame, reference)
         self.assertEquals(amr.result, reference)
+
+    def test_map_iterable(self):
+        """test map on iterables (balanced)"""
+        view = self.view
+        # 101 is prime, so it won't be evenly distributed
+        arr = range(101)
+        # so that it will be an iterator, even in Python 3
+        it = iter(arr)
+        r = view.map_sync(lambda x:x, arr)
+        self.assertEquals(r, list(arr))
+
 
     def test_abort(self):
         view = self.view

IPython/parallel/tests/test_view.py

@@ -240,6 +240,16 @@ def f(x):
         r = view.map_sync(f, data)
         self.assertEquals(r, map(f, data))
 
+    def test_map_iterable(self):
+        """test map on iterables (direct)"""
+        view = self.client[:]
+        # 101 is prime, so it won't be evenly distributed
+        arr = range(101)
+        # ensure it will be an iterator, even in Python 3
+        it = iter(arr)
+        r = view.map_sync(lambda x:x, arr)
+        self.assertEquals(r, list(arr))
+
     def test_scatterGatherNonblocking(self):
         data = range(16)
         view = self.client[:]
@@ -446,6 +456,5 @@ def check_unicode(a, check):
                     self.fail(e.evalue)
                 else:
                     raise e
-
-
+