[gdal-dev] Issue with python bindings.

[Jason Roberts]

Ivan, Frank,

 

A month ago I started a gotchas page with Even Rouault that discusses this
issue: http://trac.osgeo.org/gdal/wiki/PythonGotchas. If you have a moment,
please consider adding your examples as other cases that cause the lifetime
problem. Also (Frank) if there is any general advice you wish to add, it
would be greatly appreciated.

 

Best,

Jason

 

From: gdal-dev-bounces at lists.osgeo.org
[mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of Ivan Willig
Sent: Tuesday, October 26, 2010 10:54 AM
To: Frank Warmerdam
Cc: gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] Issue with python bindings.

 

Thanks Frank. That seems to be the issue. Whats the rule about this how long
you should keep a reference. For example this causes the same issue. 

 

ds.GetLayer().GetFeature(0).GetGeometryRef().GetEnvelope()

 

Which I am going to guess is because I should keep a reference to the
geometry. Correct? 




Ivan Willig






On Tue, Oct 26, 2010 at 10:44 AM, Frank Warmerdam <warmerdam at pobox.com>
wrote:

Ivan Willig wrote:

Hi list,
I am having an issues with using the python swig based bindings. I am on
Fedora 13 using the default gdal rpm, which is at version 1.6.2. My issue is
when i stack method calls.  For example when I do the following: 
ogr.Open("/home/ivan/dev/bigapps/data/nyco.shp").GetLayer().GetFeature(0)


I get a Segmentation fault. Here are the results of strace
http://paste.pocoo.org/show/281682/. What am I doing wrong? Should I just
hand compile a new version of gdal? Or is this not an advised usage of the
python bindings? A limitation in swig? Thanks for your help.

 

Ivan,

I believe the problem is object lifetimes.  Keep a reference to the
datasource around until you are done with the feature(s).

ds = ogr.Open("/home/ivan/dev/bigapps/data/nyco.shp")
feat = ds.GetLayer().GetFeature(0)
...
feat = None
ds = None

Best regards,
-- 
---------------------------------------+------------------------------------
--
I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

 

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