Merge pull request scikit-learn#4835 from tw991/feature2

[MRG] fix SVM can be tricked into running proba() scikit-learn#4791

Author: agramfort

sklearn/svm/base.py

@@ -571,9 +571,9 @@ def predict(self, X):
     # probabilities are not available depending on a setting, introduce two
     # estimators.
     def _check_proba(self):
-        if not self.probability:
-            raise AttributeError("predict_proba is not available when"
-                                 " probability=%r" % self.probability)
+        if not self.probability or self.probA_.size == 0 or self.probB_.size == 0:
+            raise AttributeError("predict_proba is not available when fitted with"
+                                 " probability=False")
         if self._impl not in ('c_svc', 'nu_svc'):
             raise AttributeError("predict_proba only implemented for SVC"
                                  " and NuSVC")

sklearn/svm/tests/test_svm.py

@@ -842,3 +842,13 @@ def test_lsvc_intercept_scaling_zero():
     lsvc = svm.LinearSVC(fit_intercept=False)
     lsvc.fit(X, Y)
     assert_equal(lsvc.intercept_, 0.)
+
+
+def test_trick_proba():
+    # Test that the right error message is thrown when self.probability is manually set to be True
+
+    G = svm.SVC()
+    G.fit(iris.data, iris.target)
+    G.probability = True
+    msg = "predict_proba is not available when fitted with probability=False"
+    assert_raise_message(AttributeError, msg, getattr, G, "predict_proba")