Typing `mobject.py` #4388

henrikmidtiby · 2025-08-10T19:00:58Z

Overview: What does this pull request change?

This draft PR is a work in progress to add type annotations to mobject.py.
I have created the draft PR to request some input on how to handle the remaining mypy issues.

Further Information and Comments

The following mypy errors need to be dealt with

manim/mobject/mobject.py:305: error: Cannot assign to a method  [method-assign]
manim/mobject/mobject.py:305: error: Incompatible types in assignment (expression has type "partialmethod[Any]", variable has type "Callable[[Mobject, ManimColor | int | str | tuple[int, int, int] | tuple[float, float, float] | <6 more items> | list[ManimColor | int | str | tuple[int, int, int] | tuple[float, float, float] | <6 more items>], str | None, int, Mobject | None, float], None]")  [assignment]
manim/mobject/mobject.py:308: error: Cannot assign to a method  [method-assign]
manim/mobject/mobject.py:3407: error: "Callable[..., Animation]" has no attribute "_override_animate"  [attr-defined]
manim/mobject/geometry/line.py:652: error: Argument "tip" to "add_tip" of "TipableVMobject" has incompatible type "VMobject"; expected "ArrowTip | None"  [arg-type]
manim/mobject/geometry/line.py:655: error: Argument "tip" to "add_tip" of "TipableVMobject" has incompatible type "VMobject"; expected "ArrowTip | None"  [arg-type]
manim/animation/indication.py:267: error: Argument 1 to "ShowPassingFlash" has incompatible type "Mobject"; expected "VMobject"  [arg-type]
Found 7 errors in 3 files (checked 166 source files)

Reviewer Checklist

The PR title is descriptive enough for the changelog, and the PR is labeled correctly
If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
If applicable: newly added functions and classes are tested

…2282

… code for the remaning 10 errors

henrikmidtiby · 2025-08-10T20:00:10Z

manim/mobject/geometry/line.py

+            # error: Argument "tip" to "add_tip" of "TipableVMobject" has incompatible type "VMobject"; expected "ArrowTip | None"  [arg-type]
            self.add_tip(tip=old_tips[0])
        if has_start_tip:
+            # error: Argument "tip" to "add_tip" of "TipableVMobject" has incompatible type "VMobject"; expected "ArrowTip | None"  [arg-type]
            self.add_tip(tip=old_tips[1], at_start=True)


These issues can be handled by typing.cast, but I don't think that is the best way to deal with them.

henrikmidtiby · 2025-08-10T20:02:48Z

manim/mobject/types/vectorized_mobject.py

+    def __getitem__(self, key: int) -> VMobject:
+        return self.submobjects[key]
+


This method is used to define the return type when indexing into a VGroup. If the super class was used, this would return a Mobject, but in a VGroup it should be a VMobject.

henrikmidtiby · 2025-08-10T20:05:06Z

manim/scene/vector_space_scene.py

+        temp = self.get_basis_vectors()
+        i_hat = temp.submobjects[0]
+        j_hat = temp.submobjects[1]


Apparently the trick for defining the type of elements in a VGroup to be VMobject's does not work here. Which is the reason for this workaround.

henrikmidtiby · 2025-08-10T20:06:02Z

manim/scene/vector_space_scene.py

+        temp = array.get_entries()
+        x_coord = temp.submobjects[0]
+        y_coord = temp.submobjects[1]


Apparently the trick for defining the type of elements in a VGroup to be VMobject's does not work here. Which is the reason for this workaround.

henrikmidtiby · 2025-08-10T20:06:45Z

manim/utils/color/core.py

@@ -1409,7 +1409,7 @@ def invert_color(color: ManimColorT) -> ManimColorT:
 def color_gradient(
    reference_colors: Sequence[ParsableManimColor],
    length_of_output: int,
-) -> list[ManimColor] | ManimColor:
+) -> list[ManimColor]:


Same change as in PR #4380

henrikmidtiby · 2025-08-10T20:07:00Z

manim/utils/color/core.py

@@ -1426,7 +1426,7 @@ def color_gradient(
        A :class:`ManimColor` or a list of interpolated :class:`ManimColor`'s.
    """
    if length_of_output == 0:
-        return ManimColor(reference_colors[0])
+        return [ManimColor(reference_colors[0])]


Same change as in PR #4380.

henrikmidtiby · 2025-08-10T20:11:09Z

manim/mobject/mobject.py

+    animation_overrides: dict[
+        type[Animation],
+        FunctionOverride,
+    ] = {}


By specifying the type of animation_overrides here, a lot of type errors like "type[Mobject]" has no attribute "animation_overrides" are removed.

# Conflicts: # manim/mobject/mobject.py

manim/mobject/mobject.py

@@ -1227,7 +1244,7 @@

        return self

-    def scale(self, scale_factor: float, **kwargs) -> Self:
+    def scale(self, scale_factor: float, **kwargs: Any) -> Self:


…in elements during runtime and not only during type checking

henrikmidtiby added 7 commits August 5, 2025 10:29

Add type annotations to mobject.py

af65634

More work on type annotations for mobject.py

8df3447

...

b502836

Merge branch 'main' into TypingMobject

72deed5

Almost handled all mypy errors

07e1074

Add the mypy error messages to the lines that trigger them

4af521c

Use typing.cast to avoid some mypy errors, as suggested by JasonGrace…

7183ad1

…2282

github-project-automation bot added this to Dev Board Aug 10, 2025

github-project-automation bot moved this to 🆕 New in Dev Board Aug 10, 2025

henrikmidtiby added 5 commits August 10, 2025 21:23

Used the ruff linter

d0e603e

Fixed one typing issue and added the error descriptions to the source…

acc2ff8

… code for the remaning 10 errors

Set the type of the elements in a VGroup to VMobject

01f33a0

Use typing.cast to handle some specific cases.

baf7e3d

Code cleaning

6dbfcf8

henrikmidtiby commented Aug 10, 2025

View reviewed changes

Updates

62513fd

henrikmidtiby commented Aug 10, 2025

View reviewed changes

Merge remote-tracking branch 'upstream/main' into TypingMobject

37aaa7f

# Conflicts: # manim/mobject/mobject.py

github-advanced-security bot found potential problems Aug 10, 2025

View reviewed changes

henrikmidtiby added 2 commits August 11, 2025 07:56

When started to use typing.cast it is needed to import / define certa…

107fbe2

…in elements during runtime and not only during type checking

Fix bug introduced with the type annotations.

3a2f3b5

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Typing `mobject.py` #4388

Typing `mobject.py` #4388

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		def __getitem__(self, key: int) -> VMobject:
		return self.submobjects[key]

Typing mobject.py #4388

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Overview: What does this pull request change?

Further Information and Comments

Reviewer Checklist

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Typing `mobject.py` #4388

Typing `mobject.py` #4388

henrikmidtiby commented Aug 10, 2025 •

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