QGIS python script adds populates a column with the data, but the data doesn't appear when the shapefile is opened in ArcGIS

Question

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',
'Barbastelle':'Bbl',
'Barred Tooth-striped':'BTs',
}
#etc etc      


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

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

    feature['Species'] = newStr
    layer.updateFeature(feature)

Answer 1

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

layer.commitChanges()

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