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<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#1F497D'>(Just a side note: Another way that the GDAL Python bindings
differ from typical Python libraries is the need to call gdal.UseExceptions()
to have exceptions be raised when errors occur, and the need to explicitly call
gdal.ErrorReset() in the exception handler, or the same error will keep occurring
on subsequent GDAL API calls.)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#1F497D'>Now back to the “to destroy or not to destroy”
question…<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
gdal-dev-bounces@lists.osgeo.org [mailto:gdal-dev-bounces@lists.osgeo.org] <b>On
Behalf Of </b>Jason Roberts<br>
<b>Sent:</b> Friday, September 17, 2010 3:03 PM<br>
<b>To:</b> gdal-dev@lists.osgeo.org<br>
<b>Subject:</b> [gdal-dev] With Python bindings, should geometry objects
created by ogr.Geometry() be explicitly destroyed?<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>I
have some Python code that uses OGR geometry objects internally, creating them
like this:<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>point
= ogr.Geometry(ogr.wkbPoint)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>Does
this code need to explicitly destroy these geometries, like the following, to avoid
leaks, or can it simply allow them to go out of scope and have Python’s
reference counting and garbage collector clean them up?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>point.Destroy()<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>Does
the situation change if I call feature.SetGeometry(point)? What about
feature.SetGeometryDirectly(point)?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>I’m
sorry for my ignorance here. I found a nice GDAL tutorial that seems to say
they *should* be explicitly destroyed in certain circumstances (see <a
href="http://www.gis.usu.edu/~chrisg/python/2009/lectures/ospy_slides2.pdf">http://www.gis.usu.edu/~chrisg/python/2009/lectures/ospy_slides2.pdf</a>,
page 12). But I have not really seen any other examples of this.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>If
you follow gdal-dev, you probably notice that the “to destroy or not to
destroy” question comes up periodically from Python programmers, as does
the problem where someone gets a GDALDataset, gets a band, allows the
GDALDataset to go out of scope, and then expects the band to still work. These
are areas where the GDAL Python bindings to not work like other Python
libraries, causing confusion among Python programmers, who generally expect
reference counting that “just works” and that they only need to
explicitly close something when some kind of I/O is involved.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>It
would be really great if there was FAQ that pointed out all of the ways that
GDAL differs from typical Python libraries. The scenarios I mention above seem
to be two of the most common ones. Would someone be willing to create it? I
would but do not feel competent enough at this point.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>Thanks,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'>Jason<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif"'><o:p> </o:p></span></p>
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