3b1b/manim · error · Exception

bezier cannot be calld on an empty list

Error message

bezier cannot be calld on an empty list

What it means

Raised by bezier() (utils/bezier.py:32) when called with an empty sequence of control points. A Bezier curve needs at least one control point to evaluate the Bernstein-polynomial sum, so len(points) == 0 is rejected (note the typo 'calld' in the message).

Source

Thrown at manimlib/utils/bezier.py:32

from manimlib.utils.space_ops import z_to_vector

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from typing import Callable, Sequence, TypeVar, Tuple
    from manimlib.typing import VectN, FloatArray, VectNArray, Vect3Array

    Scalable = TypeVar("Scalable", float, FloatArray)


CLOSED_THRESHOLD = 0.001


def bezier(
    points: Sequence[float | FloatArray] | VectNArray
) -> Callable[[float], float | FloatArray]:
    if len(points) == 0:
        raise Exception("bezier cannot be calld on an empty list")

    n = len(points) - 1

    def result(t: float) -> float | FloatArray:
        return sum(
            ((1 - t)**(n - k)) * (t**k) * choose(n, k) * point
            for k, point in enumerate(points)
        )

    return result


def partial_bezier_points(
    points: Sequence[Scalable],
    a: float,
    b: float
) -> list[Scalable]:
    """

View on GitHub (pinned to dee01804d4)

Solutions

1. Guard the call site: if not points: return a constant (e.g. lambda t: 0.0) instead of invoking bezier()
2. Fix the slicing/index logic so the control-point list is never empty before calling bezier()
3. If it comes from a mobject with no points, initialize/retain points on the mobject (e.g. avoid a==b in partial ranges)

Example fix

# before
curve = bezier(points[start:end])  # start >= end -> empty -> raises

# after
curve = bezier(points[start:end]) if start < end else (lambda t: points[start])

pts = points[start:end]
if len(pts) == 0:
    curve = lambda t: 0.0  # degenerate: no control points
else:
    curve = bezier(pts)

When it happens

Trigger: Directly calling bezier([]); indirectly, manim internals computing interpolants for a VMobject whose points list is empty (e.g. partial_bezier_points or get_..._interpolant on a degenerate mobject with no points).

Common situations: Feeding bezier() a slice that happens to be empty (points[i:j] with i >= j); operating on VMobjects created without points or after pointwise_become_partial with a==b producing empty slices.

Related errors

• Lines do not intersect
• Unsupported: {path_verb}
• At least 2 mobjects needed for Union.
• At least 2 mobjects needed for Intersection.
• At least 2 mobjects needed for Exclusion.

AI-assisted analysis of 3b1b/manim@dee01804d4 (2026-08-14). Data as JSON: /api/errors/d124edec382c2866. Report an issue: GitHub.