3b1b/manim · error · Exception

Invalid input sample type

Error message

Invalid input sample type

What it means

Exception('Invalid input sample type') raised in Axes.get_riemann_rectangles (manimlib/mobject/coordinate_systems.py:395). The input_sample_type keyword controls where each rectangle samples the function height and only accepts exactly 'left', 'right', or 'center'; any other string (or typo/case variant) reaches the else branch.

Source

Thrown at manimlib/mobject/coordinate_systems.py:395

        if x_range is None:
            x_range = self.x_range[:2]
        if dx is None:
            dx = self.x_range[2]
        if len(x_range) < 3:
            x_range = [*x_range, dx]

        rects = []
        x_range[1] = x_range[1] + dx
        xs = np.arange(*x_range)
        for x0, x1 in zip(xs, xs[1:]):
            if input_sample_type == "left":
                sample = x0
            elif input_sample_type == "right":
                sample = x1
            elif input_sample_type == "center":
                sample = 0.5 * x0 + 0.5 * x1
            else:
                raise Exception("Invalid input sample type")
            height_vect = self.i2gp(sample, graph) - self.c2p(sample, 0)
            rect = Rectangle(
                width=self.x_axis.n2p(x1)[0] - self.x_axis.n2p(x0)[0],
                height=get_norm(height_vect),
            )
            rect.positive = height_vect[1] > 0
            rect.move_to(self.c2p(x0, 0), DL if rect.positive else UL)
            rects.append(rect)
        result = VGroup(*rects)
        result.set_submobject_colors_by_gradient(*colors)
        result.set_style(
            stroke_width=stroke_width,
            stroke_color=stroke_color,
            fill_opacity=fill_opacity,
            stroke_behind=stroke_background
        )
        for rect in result:
            if not rect.positive:

View on GitHub (pinned to dee01804d4)

Solutions

1. Use one of the exact literals: "left", "right", or "center"
2. Normalize input before the call: value = value.strip().lower() and validate against {'left','right','center'}
3. If a custom sample point is needed, write your own rectangle loop using i2gp instead of relying on input_sample_type

Example fix

# before
rects = axes.get_riemann_rectangles(graph, input_sample_type="midpoint")

# after
rects = axes.get_riemann_rectangles(graph, input_sample_type="center")

VALID = {"left", "right", "center"}
sample_type = str(user_input).strip().lower()
assert sample_type in VALID, f"input_sample_type must be one of {VALID}, got {user_input!r}"
rects = axes.get_riemann_rectangles(graph, input_sample_type=sample_type)

def is_valid_sample_type(value: str) -> bool:
    return value in {"left", "right", "center"}

When it happens

Trigger: Calling get_riemann_rectangles(..., input_sample_type='midpoint'), 'Center', 'LEFT', or any non-literal string; passing a variable whose value drifted from the three allowed literals.

Common situations: Math convention mismatch: users write 'midpoint' or 'middle' instead of 'center'; case-sensitive copies from other libraries (matplotlib's density args); typos in scene config files.

Related errors

• At least 2 mobjects needed for Union.
• At least 2 mobjects needed for Intersection.
• At least 2 mobjects needed for Exclusion.
• Not implemented
• Mobject cannot contain self

AI-assisted analysis of 3b1b/manim@dee01804d4 (2026-08-14). Data as JSON: /api/errors/3e38bc4c92d96fe5. Report an issue: GitHub.