Python bindings: Feature.GetGeometryRef() on a temporary Python feature object doesn't keep the C++ feature object alive

[ktaylora]

Expected behavior and actual behavior.

When repairing broken geometries in Python, we make use of ogr's IsValid() and MakeValid() functions in our application code. When checking for invalid geometries, I am encountering a segfault. When I arbitrarily apply MakeValid() to the same geometries and then check for validity with IsValid(), the geometries are repaired and OGR behaves as expected. This isn't a critical bug, because we can just always call MakeValid() first on geometries we suspect are broken (see below), but it would be nice to LBYL without a segfault.

Steps to reproduce the problem.

using the following geopackage containing broken geometries that need repair.

In [1]: from osgeo import ogr
In [2]: gpkg_connection = ogr.Open("GAZ_35_New_Mexico_GU_STATEORTERRITORY.gpkg",0)
In [3]: gpkg_connection.GetLayerByIndex(0).GetName()
Out[3]: 'clippoly'
In [4]: gpkg_connection.GetLayerByIndex(0).GetFeature(1).GetGeometryRef().IsValid()
Segmentation fault

In [3]: from osgeo import ogr
In [4]: gpkg_connection = ogr.Open('GAZ_35_New_Mexico_GU_STATEORTERRITORY.gpkg', 0)
In [5]: clippoly = gpkg_connection.GetLayerByIndex(0)
In [6]: clippoly.GetFeatureCount()
Out[6]: 1
In [7]: feat = clippoly.GetFeature(1)
In [8]: geom = feat.GetGeometryRef()
In [9]: geom = geom.MakeValid()
In [10]: geom.IsValid()
Out[10]: True

Operating system

Linux *** 4.14.238-182.422.amzn2.x86_64 #1 SMP *** UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

GDAL version and provenance

GDAL (and dependencies) were compiled from source using gcc version 7.3.1 20180712 (Red Hat 7.3.1-13) (GCC). Relevant dependencies (and versions) :

GDAL_VERSION=3.3.1
SQLITE_VERSION=3350500
CMAKE_VERSION=3.12.0
POSTGRES_VERSION=11.12
PYTHON_VERSION=3.8.10
SPATIAL_INDEX_VERSION=1.9.3
FGDB_API_VERSION=1.5.1
GEOS_VERSION=3.8.1

./configure PQ_CFLAGS="-I/usr/include" PQ_LIBS="-L/usr/lib -lpq" --prefix=/usr \
--with-python \
--with-fgdb=/usr/local/filegdb_api \
--with-pg \
--with-sqlite3 \
--with-geos

[rouault]

You've hit on of the https://gdal.org/api/python_gotchas.html Change gpkg_connection.GetLayerByIndex(0).GetFeature(1).GetGeometryRef().IsValid() to f = gpkg_connection.GetLayerByIndex(0).GetFeature(1) f.GetGeometryRef().IsValid()

[ktaylora]

Thanks, Even. I shoulda Googled it.

[rouault]

I'll reopen that one as I believe we could fix that without breaking existing code (contrary to reference counting on dataset objects)