Using the Python's Script Runner plugin

The QGIS Python Script Runner plugin provides a middle ground for QGIS automation, between the interactive console and the overhead of plugins. It provides a script management dialog that allows you to easily load, create, edit, and run scripts for large-scale QGIS automation.

Getting ready

Install the Script Runner plugin using the QGIS plugin manager. Then, run the plugin from the Plugin menu to open the Script Runner dialog. Configure a default editor to edit the scripts using the following steps:

1. Find the gear icon that represents the Script Runner Preferences settings dialog box and click on it.
2. In the General Options section, check the Edit scripts using: checkbox.
3. Click on the ... button to navigate to the location of a text editor on your system.
4. Click on the Open button.
5. Click on the OK button in the Preferences dialog.

How to do it...

1. In the Script Runner dialog, click on the New Script icon, as shown in the following screenshot:
   

2. Navigate to the directory where you wish to save and name your script.
3. Verify that the new script is loaded in Script Runner.
4. Right-click (or control-click on a Mac) on the script name in Script Runner and select Edit script in external editor.
5. In the editor, replace the template code with the following code:

           from PyQt4.QtCore import * 
           from PyQt4.QtGui import * 
           from qgis.core import * 
           from qgis.gui import * 
    
           def run_script(iface): 
               layer =  QgsVectorLayer('Polygon?crs=epsg:4326', 'Mississippi',
                                       "memory") 
               pr = layer.dataProvider() 
               poly = QgsFeature() 
               geom = QgsGeometry.fromWkt("""POLYGON ((-88.82 34.99, 
                                                       -88.09 34.89, 
                                                       -88.39 30.34, 
                                                       -89.57 30.18, 
                                                       -89.73 31, 
                                                       -91.63 30.99, 
                                                       -90.87 32.37, 
                                                       -91.23 33.44, 
                                                       -90.93 34.23, 
                                                       -90.30 34.99, 
                                                       -88.82 34.99))""") 
               poly.setGeometry(geom) 
               pr.addFeatures([poly]) 
               layer.updateExtents() 
               QgsMapLayerRegistry.instance().addMapLayers([layer]) 
   

6. Click on the Run Script icon, which is represented by a green-colored arrow.
7. Close the Script Runner plugin.
8. Verify that the memory layer polygon is added to the QGIS map, as shown in the following screenshot:
   

How it works...

Script Runner is a simple but powerful idea. It allows you to build a library of automation scripts and use them from within QGIS without the overhead of building a plugin or a standalone application. All the Python and system path variables are set correctly and inherited from QGIS; however, you must still import the QGIS and Qt libraries.

There's more...

The Script Runner plugin makes managing lots of scripts easier. But there is also a script editor built into the PyQGIS console. This editor is a panel in the QGIS interface that you can use to create, edit, and run scripts. You can trigger the editor using the fourth icon from the left on the PyQGIS console toolbar.