Validate range

param/__init__.py

@@ -2378,6 +2378,32 @@ def __init__(self, default=Undefined, bounds=Undefined, softbounds=Undefined,
     def _validate(self, val):
         super(Range, self)._validate(val)
         self._validate_bounds(val, self.bounds, self.inclusive_bounds)
+        self._validate_step(val, self.step)
+        self._validate_order(val, self.step, allow_None=self.allow_None)
+
+    def _validate_step(self, val, step):
+        if step is not None:
+            if not _is_number(step):
+                raise ValueError("Step can only be None or a "
+                                 "numeric value, not type %r." % type(step))
+            elif step == 0:
+                raise ValueError("Step cannot be 0.")
+
+    def _validate_order(self, val, step, allow_None):
+        if val is None and allow_None:
+            return
+        elif val is not None and (val[0] is None or val[1] is None):
+            return
+
+        start, end = val
+        if step is not None and step > 0 and not start <= end:
+            name = "" if self.name is None else " %rs" % self.name
+            raise ValueError("Range parameter%s end %s is less than its start %s with positive step %s."
+                             % (name, end, start, step))
+        elif step is not None and step < 0 and not start >= end:
+            name = "" if self.name is None else " %rs" % self.name
+            raise ValueError("Range parameter%s start %s is less than its end %s with negative step %s."
+                             % (name, start, end, step))
 
     def _validate_bounds(self, val, bounds, inclusive_bounds):
         if bounds is None or (val is None and self.allow_None):

tests/testrangeparameter.py

@@ -156,3 +156,33 @@ def test_get_soft_bounds(self):
         q = param.Range((1,3), bounds=(0, 10), softbounds=(1, 9))
         self.assertEqual(q.get_soft_bounds(), (1, 9))
 
+    def test_validate_step(self):
+        msg = r"Step can only be None or a numeric value, not type <class 'str'>."
+
+        p = param.Range((1, 2), bounds=(0, 10), step=1)
+        with self.assertRaisesRegex(ValueError, msg):
+            q = param.Range((1, 2), bounds=(0, 10), step="1")
+
+    def test_validate_order_on_val_with_positive_step(self):
+        msg = r"Range parameter 'q's end 1 is less than its start 2 with positive step 1."
+
+        class Q(param.Parameterized):
+            q = param.Range(bounds=(0, 10), step=1)
+
+        with self.assertRaisesRegex(ValueError, msg):
+            Q.q = (2, 1)
+
+    def test_validate_order_on_val_with_negative_step(self):
+        msg = r"Range parameter 'q's start -4 is less than its end -2 with negative step -1."
+
+        class Q(param.Parameterized):
+            q = param.Range(bounds=(-5, -1), step=-1)
+
+        with self.assertRaisesRegex(ValueError, msg):
+            Q.q = (-4, -2)
+
+    def test_validate_step_order_cannot_be_0(self):
+        msg = r"Step cannot be 0."
+
+        with self.assertRaisesRegex(ValueError, msg):
+            q = param.Range(bounds=(0, 10), step=0)