Added typehints for ValueTracker (#1300)

* Added typehints

* added import

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

Author: kolibril13

manim/mobject/value_tracker.py

@@ -3,6 +3,8 @@
 __all__ = ["ValueTracker", "ExponentialValueTracker", "ComplexValueTracker"]
 
 
+from typing import Union
+
 import numpy as np
 
 from ..mobject.mobject import Mobject
@@ -52,25 +54,25 @@ def __init__(self, value=0, **kwargs):
         self.points = np.zeros((1, 3))
         self.set_value(value)
 
-    def get_value(self):
+    def get_value(self) -> float:
         """Get the current value of the ValueTracker. This value changes continuously when :attr:`animate` for the ValueTracker is called."""
         return self.points[0, 0]
 
-    def set_value(self, value):
-        """Sets a new value (float, int) to the ValueTracker"""
+    def set_value(self, value: Union[float, int]):
+        """Sets a new scalar value to the ValueTracker"""
         self.points[0, 0] = value
         return self
 
-    def increment_value(self, d_value):
-        """Increments (adds) a value (float, int) to the ValueTracker"""
+    def increment_value(self, d_value: Union[float, int]):
+        """Increments (adds) a scalar value  to the ValueTracker"""
         self.set_value(self.get_value() + d_value)
 
-    def __iadd__(self, d_value):
+    def __iadd__(self, d_value: Union[float, int]):
         """adds ``+=`` syntax to increment the value of the ValueTracker"""
         self.increment_value(d_value)
         return self
 
-    def __isub__(self, d_value):
+    def __isub__(self, d_value: Union[float, int]):
         """adds ``-=`` syntax to decrement the value of the ValueTracker"""
         self.increment_value(-d_value)
         return self