KUDU-1851 - [python] TableAlterer direct instantiation causes SIGSEGV

The python client is currently crashing when a TableAlterer is directly
instantiated as opposed to instantiating via the new_table_alterer method
in the Client class. This patch addresses this issue and includes a new
unit test.

Change-Id: I074737c8f6992a7cd21f72f711337e915ffe2e82
Reviewed-on: http://gerrit.cloudera.org:8080/5822
Reviewed-by: Todd Lipcon <[email protected]>
Tested-by: Todd Lipcon <[email protected]>

python/kudu/client.pyx

@@ -544,11 +544,7 @@ cdef class Client:
         -------
         alterer : TableAlterer
         """
-        cdef:
-            TableAlterer alterer = TableAlterer(table)
-
-        alterer._init(self.cp.NewTableAlterer(tobytes(table.name)))
-        return alterer
+        return TableAlterer(table)
 
 
 #----------------------------------------------------------------------
@@ -2563,6 +2559,8 @@ cdef class TableAlterer:
     def __cinit__(self, Table table):
         self._table = table
         self._new_name = None
+        self._init(self._table.parent.cp
+                   .NewTableAlterer(tobytes(self._table.name)))
 
     def __dealloc__(self):
         if self._alterer != NULL:

python/kudu/tests/test_client.py

@@ -345,6 +345,27 @@ def test_alter_table_add_drop_column(self):
         with self.assertRaises(KeyError):
             col = table['added-column']
 
+    def test_alter_table_direct_instantiation(self):
+        # Run the add_drop_column test with direct instantiation of
+        # the TableAlterer
+        table = self.client.table(self.ex_table)
+        alterer = kudu.client.TableAlterer(table)
+        alterer.add_column('added-column', type_='int64', default=0)
+        table = alterer.alter()
+
+        # Confirm column was added
+        expected_repr = 'Column(added-column, parent={0}, type=int64)' \
+            .format(self.ex_table)
+        self.assertEqual(expected_repr, repr(table['added-column']))
+
+        alterer = self.client.new_table_alterer(table)
+        alterer.drop_column('added-column')
+        table = alterer.alter()
+
+        # Confirm column has been dropped.
+        with self.assertRaises(KeyError):
+            col = table['added-column']
+
     def test_alter_table_add_drop_partition(self):
         # Add Range Partition
         table = self.client.table(self.ex_table)