Merging in latest boto.

boto/emr/step.py

Index: boto/emr/step.py
diff --git a/boto/emr/step.py b/boto/emr/step.py
index a444261b1aa06a2866b2fe468b9e871c279ee78c..15dfe8897f8dd1591568b16f7c175ba722a29fb4 100644
--- a/boto/emr/step.py
+++ b/boto/emr/step.py
@@ -1,4 +1,5 @@
 # Copyright (c) 2010 Spotify AB
+# Copyright (c) 2010-2011 Yelp
 #
 # Permission is hereby granted, free of charge, to any person obtaining a
 # copy of this software and associated documentation files (the
@@ -94,10 +95,11 @@ class StreamingStep(Step):
     """
     Hadoop streaming step
     """
-    def __init__(self, name, mapper, reducer=None,
+    def __init__(self, name, mapper, reducer=None, combiner=None,
                  action_on_failure='TERMINATE_JOB_FLOW',
                  cache_files=None, cache_archives=None,
-                 step_args=None, input=None, output=None):
+                 step_args=None, input=None, output=None,
+                 jar='/home/hadoop/contrib/streaming/hadoop-streaming.jar'):
         """
         A hadoop streaming elastic mapreduce step
 
@@ -107,6 +109,8 @@ class StreamingStep(Step):
         :param mapper: The mapper URI
         :type reducer: str
         :param reducer: The reducer URI
+        :type combiner: str
+        :param combiner: The combiner URI. Only works for Hadoop 0.20 and later!
         :type action_on_failure: str
         :param action_on_failure: An action, defined in the EMR docs to take on failure.
         :type cache_files: list(str)
@@ -119,15 +123,19 @@ class StreamingStep(Step):
         :param input: The input uri
         :type output: str
         :param output: The output uri
+        :type jar: str
+        :param jar: The hadoop streaming jar. This can be either a local path on the master node, or an s3:// URI.
         """
         self.name = name
         self.mapper = mapper
         self.reducer = reducer
+        self.combiner = combiner
         self.action_on_failure = action_on_failure
         self.cache_files = cache_files
         self.cache_archives = cache_archives
         self.input = input
         self.output = output
+        self._jar = jar
 
         if isinstance(step_args, basestring):
             step_args = [step_args]
@@ -135,16 +143,28 @@ class StreamingStep(Step):
         self.step_args = step_args
 
     def jar(self):
-        return '/home/hadoop/contrib/streaming/hadoop-0.18-streaming.jar'
+        return self._jar
 
     def main_class(self):
         return None
 
     def args(self):
-        args = ['-mapper', self.mapper]
+        args = []
+
+        # put extra args BEFORE -mapper and -reducer so that e.g. -libjar
+        # will work
+        if self.step_args:
+            args.extend(self.step_args)
+
+        args.extend(['-mapper', self.mapper])
+
+        if self.combiner:
+            args.extend(['-combiner', self.combiner])
 
         if self.reducer:
             args.extend(['-reducer', self.reducer])
+        else:
+            args.extend(['-jobconf', 'mapred.reduce.tasks=0'])
 
         if self.input:
             if isinstance(self.input, list):
@@ -163,17 +183,11 @@ class StreamingStep(Step):
            for cache_archive in self.cache_archives:
                 args.extend(('-cacheArchive', cache_archive))
 
-        if self.step_args:
-            args.extend(self.step_args)
-
-        if not self.reducer:
-            args.extend(['-jobconf', 'mapred.reduce.tasks=0'])
-
         return args
 
     def __repr__(self):
-        return '%s.%s(name=%r, mapper=%r, reducer=%r, action_on_failure=%r, cache_files=%r, cache_archives=%r, step_args=%r, input=%r, output=%r)' % (
+        return '%s.%s(name=%r, mapper=%r, reducer=%r, action_on_failure=%r, cache_files=%r, cache_archives=%r, step_args=%r, input=%r, output=%r, jar=%r)' % (
             self.__class__.__module__, self.__class__.__name__,
             self.name, self.mapper, self.reducer, self.action_on_failure,
             self.cache_files, self.cache_archives, self.step_args,
-            self.input, self.output)
+            self.input, self.output, self._jar)