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In Attribute Table, there is a form view instead of the table view and the label of listing on the left side can be customized using preview expression. So the user will notice a friendly and meaningful listing. I can customize it manually but I'm creating an automation plugin to load and configure from my datasets.

I observed, it gets stored as <previewExpression> of the layer in the .qgs file. However I don't see any related methods in QgsVectorLayer python class.

How can I customize the preview expression in Python?

Preview Expression

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You may use the setDisplayExpression() method from the QgsVectorLayer() class.

This method only requires a string (remember to escape the ' or the " symbols, otherwise it won't work):

layer=iface.activeLayer()

expression=' \'your expression\' '
layer.setDisplayExpression(expression)

Using an example and assuming you want to set the values of the "numbers" field as a preview expression:

enter image description here

you may use this code:

layer=iface.activeLayer()

expression=' \"numbers\" '
layer.setDisplayExpression(expression)

and you will have this result:

enter image description here

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  • Hey, that time I really looking for an answer. After a week, I just realize you already answered. I just tested it and you are right. Now I don't have to manually set it every time my script create a new layer... I wonder why I overlook the setDisplayExpression in the dir(QgsVectorLayer). Great, thanks.
    – CallMeLaNN
    Mar 21, 2017 at 16:31
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    @CallMeLaNN You're welcome. P.S. The overlooking of some crucial method when browsing a class is a common issue for me too! =)
    – mgri
    Mar 21, 2017 at 16:35

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