I know basic python, but am struggling to learn how to use it with QGIS. I have a polygon shapefile that maps the presence/absence of various species. Each species has a column in the attribute table a- if the species is present in the polygon then the species name is in the cell, otherwise "null". I have a dictionary of fullname:abbreviation which I use to create a string for each row of abbreviations so that all the data for each row is represented in a single field.

The script seems to work, but when I tried to use the shapefile in ArcGIS the new column was empty. I saved the edits afterward. Can anyone tell me what I'm missing?

from PyQt4.QtCore import QVariant

subs = {'Argent & Sable':'AS',
'Barred Tooth-striped':'BTs',
#etc etc      

layer = iface.activeLayer()
iter = layer.getFeatures()

for feature in iter:
    newStr = ''
    for field in feature.attributes():
        if field == 'NULL':
            if field in subs.keys():
                newStr += subs[field] + ', '

    feature['Species'] = newStr
  • Welcome to GIS:SE @user2980115! Do the correct values appear when you look at the attribute table in QGIS after you have saved the edits? – Joseph Feb 16 '16 at 15:10
  • I will have to check when I get home. I ran the script and used the values in QGIS but haven't tried closing and reopening the project in QGIS. I only encountered the problem when I came to work where I only have access to ArcGIS. – user2980115 Feb 16 '16 at 15:24
  • Ok, I've checked and it works fine in QGIS even if I bring it into a new project. – user2980115 Feb 16 '16 at 20:01

You are missing a call to actually save the changes back to the layer. At the end of your script you need to add:


See http://qgis.org/api/classQgsVectorLayer.html#afab34baf331320a8c3212993f5fccfa1

  • 2
    @user2980115 - You should accept this answer (click the green-faded tick on the left-hand side) to mark this question as answered =) – Joseph Feb 18 '16 at 10:29

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