SPARK-1421. Make MLlib work on Python 2.6

The reason it wasn't working was passing a bytearray to stream.write(),
which is not supported in Python 2.6 but is in 2.7. (This array came
from NumPy when we converted data to send it over to Java). Now we just
convert those bytearrays to strings of bytes, which preserves
nonprintable characters as well.

python/pyspark/mllib/__init__.py

@@ -19,11 +19,7 @@
 Python bindings for MLlib.
 """
 
-# MLlib currently needs Python 2.7+ and NumPy 1.7+, so complain if lower
-
-import sys
-if sys.version_info[0:2] < (2, 7):
-    raise Exception("MLlib requires Python 2.7+")
+# MLlib currently needs and NumPy 1.7+, so complain if lower
 
 import numpy
 if numpy.version.version < '1.7':

python/pyspark/serializers.py

@@ -64,6 +64,7 @@
 from itertools import chain, izip, product
 import marshal
 import struct
+import sys
 from pyspark import cloudpickle
 
 
@@ -113,6 +114,11 @@ class FramedSerializer(Serializer):
     where C{length} is a 32-bit integer and data is C{length} bytes.
     """
 
+    def __init__(self):
+        # On Python 2.6, we can't write bytearrays to streams, so we need to convert them
+        # to strings first. Check if the version number is that old.
+        self._only_write_strings = sys.version_info[0:2] <= (2, 6)
+
     def dump_stream(self, iterator, stream):
         for obj in iterator:
             self._write_with_length(obj, stream)
@@ -127,7 +133,10 @@ def load_stream(self, stream):
     def _write_with_length(self, obj, stream):
         serialized = self.dumps(obj)
         write_int(len(serialized), stream)
-        stream.write(serialized)
+        if self._only_write_strings:
+            stream.write(str(serialized))
+        else:
+            stream.write(serialized)
 
     def _read_with_length(self, stream):
         length = read_int(stream)