Add sanity checks for input parameters

skimage/measure/fit.py

@@ -659,6 +659,15 @@ def ransac(data, model_class, min_samples, residual_threshold,
     best_inlier_residuals_sum = np.inf
     best_inliers = None
 
+    if min_samples < 0:
+        raise ValueError("`min_samples` must be greater than zero")
+
+    if max_trials < 0:
+        raise ValueError("`max_trials` must be greater than zero")
+
+    if stop_probability < 0 or stop_probability > 1:
+        raise ValueError("`stop_probability` must be in range [0, 1]")
+
     if not isinstance(data, list) and not isinstance(data, tuple):
         data = [data]
 

skimage/measure/tests/test_fit.py

@@ -237,6 +237,19 @@ def test_ransac_dynamic_max_trials():
     assert_equal(_dynamic_max_trials(1, 100, 10, 1), float('inf'))
 
 
+def test_ransac_invalid_input():
+    assert_raises(ValueError, ransac, np.zeros((10, 2)), None, min_samples=-1,
+                                     residual_threshold=0)
+    assert_raises(ValueError, ransac, np.zeros((10, 2)), None, min_samples=2,
+                                     residual_threshold=0, max_trials=-1)
+    assert_raises(ValueError, ransac, np.zeros((10, 2)), None, min_samples=2,
+                                     residual_threshold=0,
+                                     stop_probability=-1)
+    assert_raises(ValueError, ransac, np.zeros((10, 2)), None, min_samples=2,
+                                     residual_threshold=0,
+                                     stop_probability=1.01)
+
+
 def test_deprecated_params_attribute():
     model = LineModel()
     model.params = (10, 1)