How to read/write from/to QGIS project file using Python?

Question

I'd like to save the project-dependent configuration of my Python plugin inside the QGIS project file. Is this possible and what are best practices to do so?

Answer 1

This does not work in QGIS 3.0, see answer below

Original answer

This should do it:

QgsProject.instance().writeEntry(plugin_name, property, value)

Then you just need to save the project.

Reading is performed with one of the following functions:

readEntry (plugin_name, property)
readNumEntry (plugin_name, property)
readDoubleEntry (plugin_name, property)
readBoolEntry (plugin_name, property)

Doc: http://qgis.org/api/classQgsProject.html

Answer 2

The original answer does not work in QGIS 3.x. cf https://docs.qgis.org/3.34/en/docs/pyqgis_developer_cookbook/settings.html

example from linked document:

from qgis.core import QgsSettings
def store():
   s = QgsSettings()
   s.setValue("myplugin/mytext", "hello world")
   s.setValue("myplugin/myint",  10)
   s.setValue("myplugin/myreal", 3.14)


def read():
   s = QgsSettings()
   mytext = s.value("myplugin/mytext", "default text")
   myint  = s.value("myplugin/myint", 123)
   myreal = s.value("myplugin/myreal", 2.71)
   nonexistent = s.value("myplugin/nonexistent", None)