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I've been trying to save some changes to the a dataset using PyQGIS but I can't see any changes even after closing/reloading the layer attribute table.

I have tried a few different options but none of them work.

import re
layer = iface.activeLayer()
selection = layer.getFeatures() #all features
#selection = layer.selectedFeatures() #only selected features
layer_provider=layer.dataProvider()
layer.startEditing()
for f in selection:
   text=f['RoadMntnc'] #get the unique road id to process.
   print (text)
   stext=re.split('_+', text) #split the road id into it's components.
   print(stext)
   rtype=stext[-1:] # the type of road
   newtext=' '.join(stext[:-1]) # the road name without the road type
   print (newtext)
   attr_value={2:newtext} # the column to replace and the value to use
   #layer_provider.changeAttributeValues({1:attr_value}) #attempts to write the value
   #layer.changeAttributeValue(f.id(), RoadName, 30)
   layer.changeAttributeValue(f.id(), 2, newtext)
layer.commitChanges()
layer.updateFields()

Dataset looks like enter image description here

I want to eventually autofill the RoadName, RoadType and other fields from just the unique RoadMntnc name so that there's less work/less data entry issues when adding roads to the dataset.

  • You defined rtype but never actually use it. Were you supposed to use it in the following line newtext=' '.join(rtype[:-1])? Perhaps you could edit your question to include a description of what your code is supposed to do? – Joseph Aug 8 '19 at 15:31
  • Yes, it for use to fill in other columns but I wanted to make sure the code for one column works first. The issue is that any of the 3+ formats I have tried for layer.changeAttributeValue don't actually update the table. I have edited the question with more details. – GeorgeC Aug 8 '19 at 22:37
  • Figured it out...I had to get the fieldIndex from the name of the column so the following works --- dpr = layer.dataProvider() fieldName='RoadName' fieldIndex = layer.fields().indexFromName(fieldName) dpr.changeAttributeValues({f.id(): {fieldIndex: ntext}}) – GeorgeC Aug 8 '19 at 23:09
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Here's what I ended up using

import re

def Update_Field(fieldName, ntext): # Function to simply updating fields
    print (ntext)
    fieldIndex = layer.fields().indexFromName(fieldName)
    dpr.changeAttributeValues({f.id(): {fieldIndex: ntext}})
    layer.commitChanges()
RoadType_dict = {'Rd':'Road', 'Avenue': 'Ave'}
layer = iface.activeLayer()
selection = layer.getFeatures() #all features
#selection = layer.selectedFeatures() #only selected features
dpr = layer.dataProvider()

for f in selection:
    print (f.id())
    text=f['RoadMntnc']
    print (text)
    stext=re.split('_+', text)
#Update RoadName
    ntext=' '.join(stext[:-1])
    fieldName='RoadName'
    Update_Field(fieldName,ntext)
#Update Road Type Abbreviation
    ntext=stext[-1:][0]
    fieldName='Type_Abb'
    Update_Field(fieldName,ntext)
#Update Road Type
    ntext=RoadType_dict.get(stext[-1:][0])
    fieldName='Type'
    Update_Field(fieldName,ntext)

layer.commitChanges()
layer.updateFields()
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