pyqgis - Setting a default value in a QGIS field

I would like to add in a layer's field a default value. I mean, every time a new feature is created, that field would be automatically filled with the default value.

In my case the default value would be the @project_filename variable (project's file name).

I can't find this functionality anywhere.

Regards,

Answer

Since QGIS 2.18, go to the layer properties / field properties and set an expression (@project_filename in this case) as the default value.

https://www.qgis.org/en/site/forusers/visualchangelog218/index.html#feature-client-side-default-field-values