[QGIS-Developer] QGIS standalone script examples

[Paul Wittle]

Hi folks,

I’m trying to do a simple script to open an existing project, add a layer and then save the result but finding it hard to piece together the information I can find online.

I’ve found various posts suggesting that you need to connect up the canvas or all the GUI information gets lost when you do a project.write() command but for some reason I can only find answers that contain snippets which usually seem to reference iface or canvas without showing how to initiate those in a standalone way.

Particularly, if you look at https://docs.qgis.org/3.16/en/docs/pyqgis_developer_cookbook/loadproject.html you have a note about needing to set a bridge but that references canvas which if you copy/paste as per the details in that section alone will of course result in a ‘canvas undefined’ error.

Is there a simple full example anywhere that shows how you can open a project file using a standalone python script, add one layer and save it without losing half the information in the project file?

My best effort so far added the layer but resulted in existing layers being invalid when I opened the project in QGIS and my “improved” version…at the moment…seems to be almost halving the size of the project so I assume it is still deleting all the canvas information. Any hints would be appreciated 😊

Thanks
Paul
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