[QGIS-Developer] Do QgsGeometry constGet() e constParts() return non-modifiable or modifiable reference in PyQGIS?

[Nyall Dawson]

On Fri, 12 Feb 2021 at 12:54, DelazJ <delazj at gmail.com> wrote:
>
> Hi,
>
> Le jeu. 11 févr. 2021 à 23:49, Nyall Dawson <nyall.dawson at gmail.com> a écrit :
>>
>> On Fri, 12 Feb 2021 at 05:13, Andrea Giudiceandrea
>> <andreaerdna at libero.it> wrote:
>> >
>> > Hi all,
>> > is it expected that QgsGeometry constGet() and constParts() in PyQGIS return
>> > modifiable objects?
>>
>> Yes -- python doesn't have any concept of "const", so ALL objects are
>> modifiable as a result.
>>
> So should we not pythonify the pyqgis docs (https://qgis.org/pyqgis/master/core/QgsGeometry.html#qgis.core.QgsGeometry.constParts) and avoid misleading beginners (like me in the docs PR previously mentioned)?

Yes please!

Nyall

>
> Regards,
> Harrissou
>>
>> > In the Python Console:
>> >
>> > >>> geom=QgsGeometry.fromWkt( 'Point(16 41)' )
>> > >>> geom_const=geom.constGet()
>> > >>> geom_const.transform(QgsCoordinateTransform(QgsCoordinateReferenceSystem("EPSG:4326"),
>> > >>> QgsCoordinateReferenceSystem("EPSG:25833"), QgsProject.instance()))
>> >
>> > >>> geom_const
>> > <QgsPoint: Point (584102.13444570498540998 4539238.58925933390855789)>
>> > >>> geom
>> > <QgsGeometry: Point (584102.13444570498540998 4539238.58925933390855789)>
>> >
>> >
>> > >>> geom=QgsGeometry.fromWkt( 'MultiPoint((16 41))' )
>> > >>> for part in geom.constParts():
>> >
>> > part.transform(QgsCoordinateTransform(QgsCoordinateReferenceSystem("EPSG:4326"),
>> > QgsCoordinateReferenceSystem("EPSG:25833"), QgsProject.instance()))
>> >
>> > >>> geom
>> > <QgsGeometry: MultiPoint ((584102.13444570498540998
>> > 4539238.58925933390855789))>
>>
>> Those results are as expected, but somewhat of a trap! I'd usually
>> only recommend that developers who are well aware of the dangers here
>> use the constGet method, and only do so in performance critical code
>> where they know they aren't changing the object.
>>
>> Nyall
>>
>>
>> >
>> >
>> > Regards.
>> >
>> > Andrea Giudiceandrea
>> >
>> >
>> >
>> > --
>> > Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-Developer-f4099106.html
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