I am using QGIS 2.10 (but I've also tried 2.8) to loop through all the shapefiles in a folder (those ending in .shp) and perform a dissolve function on each of them. However, when I run the following code in QGIS it crashes the program. If I run the code outside of QGIS, the QgsGeometryAnalyzer().dissolve function returns 'False'.

Strangely, the same processes work outside of a loop. For example, if I load a shapefile using the QgsVectorLayer function and perform a dissolve using the QgsGeometryAnalyzer().dissolve function everything operates correctly.

Is there something I'm missing here?

import os
from qgis.core import *
from qgis.analysis import *

files = os.listdir('C:/Temp')

for file in files:
    if file[-3:] == 'shp':
        layer = QgsVectorLayer(file, file[:-4], 'ogr')
        QgsGeometryAnalyzer().dissolve(layer, 'C:/Temp/Dissolved/' + file[:-4]+"_dissolved")

*Also, I should note that I've tried to do the same process with GRASS using the v.dissolve command. Unfortunately, this doesn't merge/dissolve polygons that are not overlapping. I need all of the polygons in a shapefile to become one multipart polygon.


Never used the QgsGeometryAnalyzer() method before (I should take a look at this) but you could use the following code which I think should do what your code does (tested this on Python Console in QGIS 2.8.2):

import processing, os, glob

result_path = "C:\Temp\Dissolved\\"

for fname in glob.glob("*.shp"):

    name= list(os.path.splitext(fname))
    name[0] = name[0] + "_dissolved"
    newName = "".join(name)
    processing.runalg('qgis:dissolve', fname, 'True', '', result_path + newName)

Hope this helps!

  • 1
    This worked! Thank you so much. The processing function seems to be a much slicker method of running QGIS tools in python. Thank you for sharing! – Joe R. Jul 14 '15 at 21:48
  • @JoeR. - Awesome buddy, glad it's working for you and most welcome! Yes, the processing function is very useful when it comes to writing commands, saves a lot of time in my opinion :) – Joseph Jul 15 '15 at 8:58

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