refinement

src/textual/_animator.py

@@ -51,8 +51,9 @@ class SimpleAnimation(Animation):
     def __call__(self, time: float) -> bool:
 
         if self.duration == 0:
-            value = self.final_value
+            setattr(self.obj, self.attribute, self.final_value)
-        else:
+            return True
+
         factor = min(1.0, (time - self.start_time) / self.duration)
         eased_factor = self.easing(factor)
 
@@ -64,9 +65,7 @@ class SimpleAnimation(Animation):
             ), "end_value must be animatable"
             value = self.start_value.blend(self.end_value, eased_factor)
         else:
-                assert isinstance(
+            assert isinstance(self.start_value, float), "`start_value` must be float"
-                    self.start_value, float
-                ), "`start_value` must be float"
             assert isinstance(self.end_value, float), "`end_value` must be float"
             if self.end_value > self.start_value:
                 eased_factor = self.easing(factor)
@@ -77,11 +76,10 @@ class SimpleAnimation(Animation):
             else:
                 eased_factor = 1 - self.easing(factor)
                 value = (
-                        self.end_value
+                    self.end_value + (self.start_value - self.end_value) * eased_factor
-                        + (self.start_value - self.end_value) * eased_factor
                 )
         setattr(self.obj, self.attribute, value)
-        return value == self.final_value
+        return factor >= 1
 
 
 class BoundAnimator:

tests/test_animator.py

@@ -22,7 +22,7 @@ class Animatable:
 
 @dataclass
 class AnimateTest:
-    """An object to animate."""
+    """An object with animatable properties."""
 
     foo: float | None = 0  # Plain float that may be set to None on final_value
     bar: Animatable = Animatable(0)  # A mock object supporting the animatable protocol
@@ -49,6 +49,8 @@ def test_simple_animation():
         easing=lambda x: x,
     )
 
+    assert animatable.foo == 0.0
+
     assert animation(time) is False
     assert animatable.foo == 20.0
 
@@ -58,7 +60,7 @@ def test_simple_animation():
     assert animation(time + 2.0) is False
     assert animatable.foo == 40.0
 
-    assert animation(time + 2.9) is False
+    assert animation(time + 2.9) is False  # Not quite final value
     assert pytest.approx(animatable.foo, 49.0)
 
     assert animation(time + 3.0) is True  # True to indicate animation is complete
@@ -89,7 +91,7 @@ def test_simple_animation_duration_zero():
         easing=lambda x: x,
     )
 
-    assert animation(time) is True
+    assert animation(time) is True  # Duration is 0, so this is last value
     assert animatable.foo == 50.0
 
     assert animation(time + 1.0) is True