Raise appropriate errors in :meth:~.VMobject.point_from_proportion (#1302)

* Raise appropriate errors in :meth:`VMobject.point_from_proportion`

* Improve docs

Co-authored-by: kolibril13 <[email protected]>
Co-authored-by: Benjamin Hackl <[email protected]>
Co-authored-by: Jason Villanueva <[email protected]>

Author: 4 people

manim/mobject/types/opengl_vectorized_mobject.py

@@ -624,7 +624,31 @@ def get_curve_functions_with_lengths(
         for n in range(num_curves):
             yield self.get_nth_curve_function_with_length(n, **kwargs)
 
-    def point_from_proportion(self, alpha):
+    def point_from_proportion(self, alpha: float) -> np.ndarray:
+        """Gets the point at a proportion along the path of the :class:`OpenGLVMobject`.
+
+        Parameters
+        ----------
+        alpha
+            The proportion along the the path of the :class:`OpenGLVMobject`.
+
+        Returns
+        -------
+        :class:`numpy.ndarray`
+            The point on the :class:`OpenGLVMobject`.
+
+        Raises
+        ------
+        :exc:`ValueError`
+            If ``alpha`` is not between 0 and 1.
+        :exc:`Exception`
+            If the :class:`OpenGLVMobject` has no points.
+        """
+
+        if alpha < 0 or alpha > 1:
+            raise ValueError(f"Alpha {alpha} not between 0 and 1.")
+
+        self.throw_error_if_no_points()
         if alpha == 1:
             return self.get_points()[-1]
 

manim/mobject/types/vectorized_mobject.py

@@ -977,20 +977,30 @@ def get_curve_functions_with_lengths(
             yield self.get_nth_curve_function_with_length(n, **kwargs)
 
     def point_from_proportion(self, alpha: float) -> np.ndarray:
-        """Get the bezier curve evaluated at a position P,
-        where P is the point corresponding to the proportion defined by the given alpha.
+        """Gets the point at a proportion along the path of the :class:`VMobject`.
 
         Parameters
         ----------
-        alpha : float
-            Proportion.
+        alpha
+            The proportion along the the path of the :class:`VMobject`.
 
         Returns
         -------
-        np.ndarray
-            Point evaluated.
+        :class:`numpy.ndarray`
+            The point on the :class:`VMobject`.
+
+        Raises
+        ------
+        :exc:`ValueError`
+            If ``alpha`` is not between 0 and 1.
+        :exc:`Exception`
+            If the :class:`VMobject` has no points.
         """
 
+        if alpha < 0 or alpha > 1:
+            raise ValueError(f"Alpha {alpha} not between 0 and 1.")
+
+        self.throw_error_if_no_points()
         if alpha == 1:
             return self.get_points()[-1]
 

tests/test_vectorized_mobject.py

@@ -20,6 +20,13 @@ def test_vmobject_point_from_propotion():
     # would be at length 3, which lands in the first, long line.
     assert np.all(obj.point_from_proportion(0.5) == np.array([3, 0, 0]))
 
+    with pytest.raises(ValueError, match="between 0 and 1"):
+        obj.point_from_proportion(2)
+
+    obj.clear_points()
+    with pytest.raises(Exception, match="with no points"):
+        obj.point_from_proportion(0)
+
 
 def test_vgroup_init():
     """Test the VGroup instantiation."""