How to open, modify and save a QGIS project with PYQGIS

Question

I need to create a stand-alone script for opening a QGIS template project, modify a layer data source, export the Composition and finally save the modified .qgs project into a new file. So far I have only found some examples for QGIS plugins, but of course they don't work for the stand-alone uses. Can anybody give me some helpful hints? Thanks!

Answer 1

1. you can use PyQGIS from outside QGIS (search in gis.stackexchange)
2. otherwise, a QGIS project file ( .qgs) is a simple XML file and there are many Python modules to process XML files:

part of a .qgs/XML file:

from xml.etree import ElementTree as ET 
with open('test.qgs', 'r') as f:
     tree  = ET.parse(f)
     for elem in tree.findall('.//mapcanvas'):
         print("units: "), elem.find('units').text
 units :  meters
 .....