[SPARK-20631][PYTHON][ML] LogisticRegression._checkThresholdConsistency should use values not Params

## What changes were proposed in this pull request?

- Replace `getParam` calls with `getOrDefault` calls.
- Fix exception message to avoid unintended `TypeError`.
- Add unit tests

## How was this patch tested?

New unit tests.

Author: zero323 <[email protected]>

Closes #17891 from zero323/SPARK-20631.

(cherry picked from commit 804949c)
Signed-off-by: Yanbo Liang <[email protected]>

Author: zero323

python/pyspark/ml/classification.py

@@ -200,13 +200,13 @@ def getThresholds(self):
 
     def _checkThresholdConsistency(self):
         if self.isSet(self.threshold) and self.isSet(self.thresholds):
-            ts = self.getParam(self.thresholds)
+            ts = self.getOrDefault(self.thresholds)
             if len(ts) != 2:
                 raise ValueError("Logistic Regression getThreshold only applies to" +
                                  " binary classification, but thresholds has length != 2." +
-                                 " thresholds: " + ",".join(ts))
+                                 " thresholds: {0}".format(str(ts)))
             t = 1.0/(1.0 + ts[0]/ts[1])
-            t2 = self.getParam(self.threshold)
+            t2 = self.getOrDefault(self.threshold)
             if abs(t2 - t) >= 1E-5:
                 raise ValueError("Logistic Regression getThreshold found inconsistent values for" +
                                  " threshold (%g) and thresholds (equivalent to %g)" % (t2, t))

python/pyspark/ml/tests.py

@@ -765,6 +765,18 @@ def test_logistic_regression(self):
         except OSError:
             pass
 
+    def logistic_regression_check_thresholds(self):
+        self.assertIsInstance(
+            LogisticRegression(threshold=0.5, thresholds=[0.5, 0.5]),
+            LogisticRegressionModel
+        )
+
+        self.assertRaisesRegexp(
+            ValueError,
+            "Logistic Regression getThreshold found inconsistent.*$",
+            LogisticRegression, threshold=0.42, thresholds=[0.5, 0.5]
+        )
+
     def _compare_params(self, m1, m2, param):
         """
         Compare 2 ML Params instances for the given param, and assert both have the same param value