In a academic project I've produced a small python script for watershed analysis. This script relates shapefiles attributes and generates a .txt file.

I am trying to adjust the script to use within the QGIS environment. When I use it, it shows the following error:

unsupported operand type (s) for /: 'int' and 'list' See log for more details

In logs we can see:

2019-01-03T21:10:57 2   Uncaught error while executing algorithm
        Traceback (most recent call last):
          File "C:/PROGRA~1/QGIS2~1.18/apps/qgis-ltr/./python/plugins\processing\core\GeoAlgorithm.py", line 203, in execute
          File "C:/PROGRA~1/QGIS2~1.18/apps/qgis-ltr/./python/plugins\processing\script\ScriptAlgorithm.py", line 381, in processAlgorithm
            exec((script), ns)
          File "<string>", line 123, in <module>
          File "<string>", line 35, in densidade_rios
        TypeError: unsupported operand type(s) for /: 'int' and 'list'

Here is the code:

from qgis.core import *
import math

# Function    
def densidade_rios(valor_total_rios, valor_area_bacia):
    dr = valor_total_rios / valor_area_bacia
    return dr

# Loading dreinage and watershed layers
dlayer = QgsVectorLayer(Drenagem, "drenagem", "ogr")
blayer = QgsVectorLayer(Bacia, "bacia", "ogr")

# Dreinage attributes
dfeatures = dlayer.getFeatures()
# Listing values per column
listdfeatures = list(zip(*dfeatures))

# Max and min order values
maxordem = max(listdfeatures[0])
minordem = min(listdfeatures[0])

# Counting features of channel hierarchy (dreinage layer values)
ordem = minordem
hierarquia = []
while (ordem <= maxordem):
    contagem = listdfeatures[0].count(ordem)
    ordem += 1

# Total of rivers - quantity of first order rivers (dreinage layer values)
totalrios = hierarquia[0]

# Watershed attributes    
areabh = blayer.getValues(blayer.fields()[0].name())[0]

# Using function    
dr = densidade_rios(totalrios, areabh)

Attribute table values of drenagem layer:

enter image description here

Attribute table values of bacia layer:

enter image description here

  • 2
    What is the value of areabh = blayer.getValues(blayer.fields()[0].name())[0] ? Perhaps that line has changed and the last [0] has been forgotten. I can't fully understand what it's trying to do, the comments are in a language that I don't know. Both values should be a number type but the 2nd one is a list object at that line. – Michael Stimson Jan 4 at 0:44
  • 2
    @MichaelStimson you are right. I need one more [0] in the line areabh = blayer.getValues(blayer.fields()[0].name())[0] to take the value of the list. Because of this it wasn't working, because I was taking all the list, not one value of the list. So, the code have to be areabh = blayer.getValues(blayer.fields()[0].name())[0][0]. Problem solved, the code is working! Thank you! – Carolina Jan 4 at 14:24

As mentioned by Michael Stimson the error is because a list was used where a number was expected.

densidade_rios is returning the result of a division, hence areabh (which is the division's denominator) needs to be a value:

areabh = blayer.getValues('Area_km2')[0][0] # where 'blayer.fields()[0].name()' is the field name 'Area_km2'.

Another way of getting areabh would be:

areabh = [f['Area_km2'] for f in blayer.getFeatures()][0]

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.