[PyQt] Using __hash__ functions for custom classes

Phil Thompson phil at riverbankcomputing.com
Tue Mar 31 09:29:09 BST 2020

On 31/03/2020 01:58, Stephen Knox wrote:
> Noob question here.
> Is there any guidance on how to implement __hash__ functions for custom
> classes. Should they be generated automatically if there is a qHash
> function?
> I am trying specifically to debug this issue:
> https://github.com/qgis/QGIS/issues/29225, which is caused by the
> QgsActionScope class not having a hash function. There is an __eq__
> function but no __hash__ function.
> Code is at
> https://github.com/qgis/QGIS/blob/master/src/core/qgsactionscope.cpp,
> https://github.com/qgis/QGIS/blob/master/src/core/qgsactionscope.h and
> https://github.com/qgis/QGIS/blob/master/python/core/auto_generated/qgsactionscope.sip.in
> .
> I have tried implementing a special-method in the sip.in file but can't
> seem to get the syntax right, and I am unsure whether this is necessary 
> or
> not.

You have to implement __hash__ yourself where you need it. There are 
plenty of examples in the PyQt .sip files.


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