2

I am trying to add new field to my table based on two other existing fields. In the field Calculator it's quite simple:

My Goal

When I am trying to run as a Python code I got into trouble, Here's my code:

vLayer = iface.activeLayer()    
vLayer.dataProvider().addAttributes([QgsField('1m_Cases', QVariant.Int)])
vLayer.updateFields()
for f in vLayer.getFeatures(): 
        f.setAttribute(f.fieldNameIndex('1m_Cases'), f(['J_TotalCases'] *1000000)/ f['Pop'])
vLayer.commitChanges()    
0

2 Answers 2

2

you can change the code like below, which should work:

vLayer = iface.activeLayer()
vLayer.dataProvider().addAttributes([QgsField('1m_Cases', QVariant.Int)])
vLayer.updateFields()
vLayer.startEditing()
for f in vLayer.getFeatures():
    f['1m_Cases'] = f['J_TotalCases'] *1000000/ f['Pop']
    vLayer.updateFeature(f)
vLayer.commitChanges()   
4
  • Can you not mix the use of dataprovider and editing session? Either use only the dataprovider or the editing buffer. Thanks
    – etrimaille
    Commented Apr 16, 2020 at 7:19
  • I tried to run the code but I got the error: TypeError: unsupported operand type(s) for *: 'QVariant' and 'int'??
    – user130952
    Commented Apr 18, 2020 at 0:41
  • 1
    I've tried the code, but there was no error. The error indicates, that in the line with f['J_TotalCases'] *1000000/ f['Pop'] something goes wrong. May be you'll try: from PyQt5.QtCore import QVariant
    – eurojam
    Commented Apr 18, 2020 at 4:57
  • Thanks it was a mistype on my end. It's working now
    – user130952
    Commented Apr 19, 2020 at 20:11
2

Based on the answer from @eurojam but using only the editing buffer, like in QGIS GUI.

from qgis.core import edit

vLayer = iface.activeLayer()
with edit(vLayer)
    vLayer.addAttribute(QgsField('1m_Cases', QVariant.Int))
    for f in vLayer.getFeatures():
        f['1m_Cases'] = f['J_TotalCases'] *1000000/ f['Pop']
        vLayer.updateFeature(f)
1
  • Thanks for your quick help, will try it now...
    – user130952
    Commented Apr 16, 2020 at 18:46

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