[SPARK-10509][PYSPARK] Reduce excessive param boiler plate code

The current python ml params require cut-and-pasting the param setup and description between the class & ```__init__``` methods. Remove this possible case of errors & simplify use of custom params by adding a ```_copy_new_parent``` method to param so as to avoid cut and pasting (and cut and pasting at different indentation levels urgh).

Author: Holden Karau <holden@us.ibm.com>

Closes #10216 from holdenk/SPARK-10509-excessive-param-boiler-plate-code.

1 files changed, 12 insertions, 0 deletions

diff --git a/python/pyspark/ml/tests.py b/python/pyspark/ml/tests.py
index 9ea639dc4f..c45a159c46 100644
--- a/python/pyspark/ml/tests.py
+++ b/python/pyspark/ml/tests.py
@@ -185,6 +185,18 @@ class OtherTestParams(HasMaxIter, HasInputCol, HasSeed):
 
 class ParamTests(PySparkTestCase):
 
+    def test_copy_new_parent(self):
+        testParams = TestParams()
+        # Copying an instantiated param should fail
+        with self.assertRaises(ValueError):
+            testParams.maxIter._copy_new_parent(testParams)
+        # Copying a dummy param should succeed
+        TestParams.maxIter._copy_new_parent(testParams)
+        maxIter = testParams.maxIter
+        self.assertEqual(maxIter.name, "maxIter")
+        self.assertEqual(maxIter.doc, "max number of iterations (>= 0).")
+        self.assertTrue(maxIter.parent == testParams.uid)
+
     def test_param(self):
         testParams = TestParams()
         maxIter = testParams.maxIter