matplotlib/matplotlib · error · ValueError

x and y must be equal-length 1D arrays, but found shapes {se

Error message

x and y must be equal-length 1D arrays, but found shapes {self.x.shape!r} and {self.y.shape!r}

What it means

Error "x and y must be equal-length 1D arrays, but found shapes {self.x.shape!r} and {self.y.shape!r}" thrown in matplotlib/matplotlib.

Source

Thrown at lib/matplotlib/tri/_triangulation.py:48

        take the *mask* into account, use `get_masked_triangles` instead.
    mask : (ntri, 3) array of bool or None
        Masked out triangles.
    is_delaunay : bool
        Whether the Triangulation is a calculated Delaunay
        triangulation (where *triangles* was not specified) or not.

    Notes
    -----
    For a Triangulation to be valid it must not have duplicate points,
    triangles formed from colinear points, or overlapping triangles.
    """
    def __init__(self, x, y, triangles=None, mask=None):
        from matplotlib import _qhull

        self.x = np.asarray(x, dtype=np.float64)
        self.y = np.asarray(y, dtype=np.float64)
        if self.x.shape != self.y.shape or self.x.ndim != 1:
            raise ValueError("x and y must be equal-length 1D arrays, but "
                             f"found shapes {self.x.shape!r} and "
                             f"{self.y.shape!r}")

        self.mask = None
        self._edges = None
        self._neighbors = None
        self.is_delaunay = False

        if triangles is None:
            # No triangulation specified, so use matplotlib._qhull to obtain
            # Delaunay triangulation.
            self.triangles, self._neighbors = _qhull.delaunay(x, y, sys.flags.verbose)
            self.is_delaunay = True
        else:
            # Triangulation specified. Copy, since we may correct triangle
            # orientation.
            try:
                self.triangles = np.array(triangles, dtype=np.int32, order='C')

View on GitHub (pinned to b379c1b69e)

When it happens

Trigger: Thrown at lib/matplotlib/tri/_triangulation.py:48 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of matplotlib/matplotlib@b379c1b69e (2026-08-21). Data as JSON: /api/errors/42adf0dc8beda5d4. Report an issue: GitHub.