How to delete user defined project variables using Python

Question

I am trying to delete a variable from QGIS Project variables. I didn't find the functionality in QgsExpressionContextUtils (I use it to set a variable). I also tried to do this:

project_context_scope = QgsExpressionContextUtils.projectScope()
project_context_scope.removeVariable('test')

It does remove from project_context_scope. But, when I open the QGIS Project properties to see the list of variables, the deleted variable is still exist.

May be I was wrong in getting the instance of project_context_scope, since it's not a singleton and projectScope create new object.

Did you try with del variable_name? If you have a list: for var in list:...del var. — xunilk, Jul 24 '17 at 17:40
I don't think that will work since the variable_name is a string. It's like value mapping. — ismailsunni, Jul 25 '17 at 01:07

ismailsunni · Accepted Answer · 2023-08-11T03:10:19.357

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I have found a way to do it, after got suggestion from nwadson's comment

The idea is using QgsExpressionContextUtils.projectScope().variableNames() to get existing variables. Then iterate which variable that you want to keep. After that, you set it with:

QgsExpressionContextUtils.setProjectVariables(existing_variables)

Note: there is no high-level API to delete a project variable for now.

Update: I have implemented the API to do it (like @martin mentioned on the other answer)

edited Aug 11 '23 at 03:10

answered Jul 25 '17 at 02:10

ismailsunni

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Don't forget to accept your answer by clicking the green-faded tick on the left-hand side :) – Joseph Nov 30 '17 at 12:06

score 1 · Answer 2 · answered Aug 10 '23 at 15:05

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In QGIS 3 this functionality is added, simply use:

QgsExpressionContextUtils.removeProjectVariable(QgsProject.instance(), 'your_project_variable_name')

answered Aug 10 '23 at 15:05

Martin

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ah yes, I ended up implementing the API. Thanks for reminding me. – ismailsunni Aug 11 '23 at 03:11

score 0 · Answer 3 · answered Jul 25 '17 at 12:56

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I'm not sure about your use case, but one option is since the .qgs file is just xml you could open the file with python and do a simple .replace then save out each line to a new .qgs file, delete old .qgs file, and rename new back to old .qgs filename.

answered Jul 25 '17 at 12:56

artwork21

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Thanks for the answer. But, for my use case, it won't work since the QGIS project is on the fly. – ismailsunni Jul 26 '17 at 01:02
@ismailsunni, can you expand more what you mean by "it won't work since the QGIS project is on the fly"? – artwork21 Jul 26 '17 at 11:55
Ah sorry for not so clear reply. So, in my use case, I do not work with the qgs file, but more in the project variable when we run QGIS. I am not sure, but if we updated the .qgs file, we should reload / refresh the project in QGIS. In my case, I can't do that (or may be it's too complicated) – ismailsunni Jul 26 '17 at 15:57

How to delete user defined project variables using Python

3 Answers3