A few bits of cleanup

mobject/vectorized_mobject.py

@@ -100,12 +100,12 @@ class VMobject(Mobject):
         #match styles accordingly
         submobs1, submobs2 = self.submobjects, vmobject.submobjects
         if len(submobs1) == 0:
-            return
+            return self
         elif len(submobs2) == 0:
             submobs2 = [vmobject]
         for sm1, sm2 in zip(*make_even(submobs1, submobs2)):
             sm1.match_style(sm2)
-        return
+        return self
 
     def fade(self, darkness = 0.5):
         for submob in self.submobject_family():

topics/geometry.py

@@ -97,9 +97,6 @@ class Arc(VMobject):
         return self
 
 
-
-
-
 class Circle(Arc):
     CONFIG = {
         "color" : RED,
@@ -511,6 +508,7 @@ class Arrow(Line):
         Line.put_start_and_end_on(self, *args, **kwargs)
         self.set_tip_points(self.tip, preserve_normal = False)
         self.set_rectangular_stem_points()
+        return self
 
     def scale(self, scale_factor, **kwargs):
         Line.scale(self, scale_factor, **kwargs)
@@ -520,6 +518,9 @@ class Arrow(Line):
             self.set_rectangular_stem_points()
         return self
 
+    def copy(self):
+        return self.deepcopy()
+
 class Vector(Arrow):
     CONFIG = {
         "color" : YELLOW,

topics/number_line.py

@@ -200,14 +200,21 @@ class Axes(VGroup):
             self.y_axis.point_to_number(point),
         )
 
-    def get_graph(self, function, num_graph_points = None, **kwargs):
+    def get_graph(
+        self, function, num_graph_points = None, 
+        x_min = None,
+        x_max = None,
+        **kwargs
+        ):
         kwargs["fill_opacity"] = kwargs.get("fill_opacity", 0)
         kwargs["num_anchor_points"] = \
             num_graph_points or self.default_num_graph_points
+        x_min = x_min or self.x_min
+        x_max = x_max or self.x_max
         graph = ParametricFunction(
             lambda t : self.coords_to_point(t, function(t)),
-            t_min = self.x_min,
-            t_max = self.x_max,
+            t_min = x_min,
+            t_max = x_max,
             **kwargs
         )
         graph.underlying_function = function