Buffering in PyQGIS

You have different ways to get what you want by PyQGIS Console:

1. Aragon's suggestion;
2. by using QgsGeometryAnalyzer class:

from qgis.utils import iface from qgis.analysis import QgsGeometryAnalyzer mc = iface.mapCanvas() layer = mc.currentLayer() QgsGeometryAnalyzer().buffer(layer, "path_to/output.shp", 500, False, False, -1) 

1. by using Sextante class:

from sextante.core.Sextante import Sextante Sextante.runalg("ftools:fixeddistancebuffer","input_path.shp", False, 500, 5, True, "output_path_buffer.shp") 

To get the sextante parameters type Sextante.alghelp("ftools:fixeddistancebuffer") in PyQGIS Console.

Hope this helps !

if you want basic code, you can try:

#Don't forget to Toggle Editing lyr = qgis.utils.iface.activeLayer() provider = lyr.dataProvider() feat= QgsFeature() alls = provider.attributeIndexes() provider.select(alls) while provider.nextFeature(feat): buff = feat.geometry().buffer(5,2) lyr.dataProvider().changeGeometryValues({feat.id(): buff}) 

Just a little thing to add to the last reply.

To search for a SEXTANTE algorithm about a given topic, use Sextante.alglist(). For instance, in the case of searching for something containing "buffer", you would do

>>> from sextante.core.Sextante import Sextante >>> Sextante.alglist("buffer") 

And you would get:

Grid Buffer------------------------------------------>saga:gridbuffer Grid Proximity Buffer-------------------------------->saga:gridproximitybuffer Shapes Buffer---------------------------------------->saga:shapesbuffer Threshold Buffer------------------------------------->saga:thresholdbuffer Fixed distance buffer-------------------------------->ftools:fixeddistancebuffer Variable distance buffer----------------------------->ftools:variabledistancebuffer r.buffer - Creates a raster map layer showing buffer zones surrounding cells that contain non-NULL category values.--->grass:r.buffer v.buffer.angle--------------------------------------->grass:v.buffer.angl v.buffer.column - Creates a buffer around features of given type.--->grass:v.buffer.column v.buffer.distance - Creates a buffer around features of given type.--->grass:v.buffer.distance v.buffer.minordistance------------------------------->grass:v.buffer.minordistance 

That way, you can find the name of the algorithm to call (ftools:fixeddistancebuffer, in the example proposed in the reply above)

You can turn your script into a new algorithm in SEXTANTE. The SEXTANTE documentation has detailed information about that.