ARROW-2065: [Python] Fix bug in SerializationContext.clone().

One issue is that I don't think the test fails on the current master.

Author: Robert Nishihara <robertnishihara@gmail.com>

Closes apache#1539 from robertnishihara/fixclonebug and squashes the following commits:

61534b8 [Robert Nishihara] Fix test.
35a559a [Robert Nishihara] Fix bug in which SerializationContext.clone() doesn't copy a field.

python/pyarrow/serialization.pxi

@@ -89,6 +89,7 @@ cdef class SerializationContext:
  result = SerializationContext()
  result.type_to_type_id = self.type_to_type_id.copy()
  result.whitelisted_types = self.whitelisted_types.copy()
+ result.types_to_pickle = self.types_to_pickle.copy()
  result.custom_serializers = self.custom_serializers.copy()
  result.custom_deserializers = self.custom_deserializers.copy()
  result.pickle_serializer = self.pickle_serializer

python/pyarrow/tests/test_serialization.py

@@ -248,6 +248,33 @@ def large_memory_map(tmpdir_factory, size=100*1024*1024):
  return path
 
 
+def test_clone():
+ context = pa.SerializationContext()
+
+ class Foo(object):
+ pass
+
+ def custom_serializer(obj):
+ return 0
+
+ def custom_deserializer(serialized_obj):
+ return (serialized_obj, 'a')
+
+ context.register_type(Foo, 'Foo', custom_serializer=custom_serializer,
+ custom_deserializer=custom_deserializer)
+
+ new_context = context.clone()
+
+ f = Foo()
+ serialized = pa.serialize(f, context=context)
+ deserialized = serialized.deserialize(context=context)
+ assert deserialized == (0, 'a')
+
+ serialized = pa.serialize(f, context=new_context)
+ deserialized = serialized.deserialize(context=new_context)
+ assert deserialized == (0, 'a')
+
+
 def test_primitive_serialization(large_buffer):
  for obj in PRIMITIVE_OBJECTS:
  serialization_roundtrip(obj, large_buffer)