I want to use a loop to select values with expression in a layer. The values contain the letters OS and a number (example: "OS1","OS2"). I want to use the loop to increase the number to use my processing script on the features separately. How do I use the selectbyexpression() in the right way to increase the number in a loop?

i = 1
OSnumber = str(i)
OSname = 'OS'+OSnumber

OS_trace = Map+'OS_tracés.shp'
layer = iface.activeLayer()
layer.selectByExpression("attributename = 'Osname'")

1 Answer 1


You can use the following script structure:

layer = iface.activeLayer()

end_number = 5 # OS1, OS2, OS3, OS4, OS5
attribute_name = "attribute_name" # field name containing OS values

for i in range(end_number):
    osname = f"OS{i+1}"
    layer.selectByExpression(f"{attribute_name} = '{osname}'")

    # Do whatever with the selected features
    # For example:

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