[Gdal-dev] References and scripting language bindings

[Frank Warmerdam]

On 9/15/05, Ari Jolma <ari.jolma at tkk.fi> wrote:
> Hi, this problem was discussed on IRC yesterday but I'm slow to
> understand, so I try to describe the problem again and think about a
> solution.
> 
> The problem is that if you do something like
> 
> layer = datasource.Open('data').GetLayerByIndex(0)
> print layer.Name

Ari,

To clarify for the list the problem you point out has 
existed in the Python OGR bindings (and for that matter
in the GDAL bindings) as long as they have existed.  The
requirement so far has been for the script writer to keep
a reference to the datasource until they are done using 
objects owned by the datasource such as layers (or bands
in GDAL's case). 

While this is not a terrible onerous requirement, it does violate
the reasonable expectation of the scripter, and introduces an
easy way to cause unexpected crashes which is undesirable. 

So, the "safe" version of your code would be:

ds = ogr.Open("data")
layer = layer.GetLayerByIndex(0)
... do stuff with layer

ds = None  
l
Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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