django/django · error · IndexError

Index out of range when accessing points of a line string: %

Error message

Index out of range when accessing points of a line string: %s.

What it means

Raised as IndexError by LineString.__getitem__ when the requested index is outside [0, point_count) (geometries.py:657). It guards the underlying OGR get_point C call from an out-of-bounds read.

Source

Thrown at django/contrib/gis/gdal/geometries.py:657

class LineString(OGRGeometry):
    def __getitem__(self, index):
        "Return the Point at the given index."
        if 0 <= index < self.point_count:
            x, y, z, m = c_double(), c_double(), c_double(), c_double()
            capi.get_point(self.ptr, index, byref(x), byref(y), byref(z), byref(m))
            if self.is_3d and self.is_measured:
                return x.value, y.value, z.value, m.value
            if self.is_3d:
                return x.value, y.value, z.value
            if self.is_measured:
                return x.value, y.value, m.value
            dim = self.coord_dim
            if dim == 1:
                return (x.value,)
            elif dim == 2:
                return (x.value, y.value)
        else:
            raise IndexError(
                "Index out of range when accessing points of a line string: %s." % index
            )

    def __len__(self):
        "Return the number of points in the LineString."
        return self.point_count

    @property
    def tuple(self):
        "Return the tuple representation of this LineString."
        return tuple(self[i] for i in range(len(self)))

    coords = tuple

    def _listarr(self, func):
        """
        Internal routine that returns a sequence (list) corresponding with
        the given function.

View on GitHub (pinned to ae25a40be0)

Solutions

1. Bounds-check before indexing: if 0 <= i < len(line): ...
2. Use negative-safe iteration: for pt in line.tuple: ...
3. Cache len(line) / line.point_count and clamp the index.

Example fix

// before
last = line[len(line)]  # off-by-one -> IndexError

// after
last = line[len(line) - 1]

def safe_line_point(line, i):
    if not (0 <= i < len(line)):
        raise IndexError(f'vertex {i} out of range [0,{len(line)})')
    return line[i]

def is_valid_line_index(line, i) -> bool:
    return isinstance(i, int) and 0 <= i < len(line)

try:
    pt = line[i]
except IndexError:
    pt = None  # or clamp i to range

When it happens

Trigger: Calling line[i] where i < 0 or i >= line.point_count; iterating with a hard-coded index larger than the actual vertex count; off-by-one when computing the last vertex.

Common situations: Parsing geometries of varying vertex counts and assuming a fixed length; index derived from user input without bounds checking; reverse iteration using positive indices.

Related errors

• Index out of range when accessing rings of a polygon: %s.
• Index out of range when accessing geometry in a collection:
• Negative indices are not allowed on OGR Layers.
• Index out of range when accessing layers in a datasource: %s
• Invalid index type: %s

AI-assisted analysis of django/django@ae25a40be0 (2026-08-06). Data as JSON: /api/errors/ab2b70709939c2aa. Report an issue: GitHub.