Backport PR #5766: View.map with empty sequence should return empty list

closes  #5765

IPython/parallel/client/remotefunction.py

@@ -1,20 +1,7 b''
-"""Remote Functions and decorators for Views.
+"""Remote Functions and decorators for Views."""
 
-Authors:
-
-* Brian Granger
-* Min RK
-"""
-#-----------------------------------------------------------------------------
-#  Copyright (C) 2010-2011  The IPython Development Team
-#
-#  Distributed under the terms of the BSD License.  The full license is in
-#  the file COPYING, distributed as part of this software.
-#-----------------------------------------------------------------------------
-
-#-----------------------------------------------------------------------------
-# Imports
-#-----------------------------------------------------------------------------
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
 
 from __future__ import division
 
@@ -203,6 +190,10 b' class ParallelFunction(RemoteFunction):'
                 minlen = n
             lens.append(n)
         
+        if maxlen == 0:
+            # nothing to iterate over
+            return []
+        
         # check that the length of sequences match
         if not self._mapping and minlen != maxlen:
             msg = 'all sequences must have equal length, but have %s' % lens

IPython/parallel/tests/test_view.py

@@ -1,20 +1,8 b''
 # -*- coding: utf-8 -*-
-"""test View objects
+"""test View objects"""
 
-Authors:
-
-* Min RK
-"""
-#-------------------------------------------------------------------------------
-#  Copyright (C) 2011  The IPython Development Team
-#
-#  Distributed under the terms of the BSD License.  The full license is in
-#  the file COPYING, distributed as part of this software.
-#-------------------------------------------------------------------------------
-
-#-------------------------------------------------------------------------------
-# Imports
-#-------------------------------------------------------------------------------
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
 
 import base64
 import sys
@@ -347,6 +335,11 b' class TestView(ClusterTestCase):'
         r = view.map_sync(f, data)
         self.assertEqual(r, list(map(f, data)))
     
+    def test_map_empty_sequence(self):
+        view = self.client[:]
+        r = view.map_sync(lambda x: x, [])
+        self.assertEqual(r, [])
+    
     def test_map_iterable(self):
         """test map on iterables (direct)"""
         view = self.client[:]