PyQGIS Error – Fix AttributeError: ‘NoneType’ Object Has No Attribute ‘selectByExpression’

Question

I get the error: AttributeError: 'NoneType' object has no attribute 'selectByExpression'

The first run through the loop is fine but at the second run the error occurs.

How do I fix this?

import processing
import os
import shutil
import time

t_begin = time.localtime()
print(time.strftime('%H:%M:%S', t_begin))

input = 'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/PDots.shp'
N=0


while(N<10):
    print("N="+str(N))
    outFile = 'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/temp_buffer'+str(N)+'.shp'
    layer = iface.addVectorLayer(input,'','ogr')
   # geselecteerd1 = layer.selectByExpression("kleur = 'blue'")
    geselecteerd1= layer.selectByExpression("kleur = 'blue'")
    #puntlaag voor buffer maken########################################################
    BufferFile = 'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/buffer'+str(N)+'.shp'
    #print(BufferFile)

    writer = QgsVectorFileWriter.writeAsVectorFormat(layer,BufferFile,'utf-8',
    driverName = 'ESRI Shapefile', onlySelected= True)

    #selected_layer1 = iface.addVectorLayer(BufferFile,'','ogr')
    del(writer)

    #buffer maken met puntlaag "BufferFile"###########################################
    processing.run("native:buffer", {'INPUT':'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/buffer'+str(N)+'.shp',
    'DISTANCE':30,'SEGMENTS':5,'END_CAP_STYLE':0,'JOIN_STYLE':0,
    'MITER_LIMIT':2,'DISSOLVE':False,
    'OUTPUT':outFile})

    #iface.addVectorLayer(outFile,'','ogr') #voeg bufferlaag toe aan kaart

    layer.removeSelection()
    geselecteerd2 = layer.selectByExpression("kleur = 'red'")

    #puntlaag maken van rode punten####################################################
    RedDots = 'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/RedDots'+str(N)+'.shp'
    writer = QgsVectorFileWriter.writeAsVectorFormat(layer,RedDots,'utf-8',
    driverName = 'ESRI Shapefile', onlySelected= True)

    #selected_layer2 = iface.addVectorLayer(RedDots,'','ogr')
    del(writer)

    #layer.removeSelection()

    #rode punten in buffer tellen#######################################################
    CountFile = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/temp_count"+str(N)+".shp"
    if (N==2):
        processing.run("native:createspatialindex", {'INPUT':RedDots})
    else:
        processing.run("native:createspatialindex", {'INPUT':RedDots})

    processing.run("native:countpointsinpolygon",{
    'POLYGONS':outFile,
    'POINTS':RedDots,
    'WEIGHT':'','CLASSFIELD':'','FIELD':'NUMPOINTS2',
    'OUTPUT':CountFile})

    #iface.addVectorLayer(CountFile,'','ogr')

    #punten maken van polygoon punten tellen################################################
    NewDots = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/NewDots"+str(N)+".shp"
    processing.run("native:centroids", 
    {'INPUT': CountFile,'ALL_PARTS':True,'OUTPUT':NewDots})

    iface.addVectorLayer(NewDots,'','ogr')

    # blauw naar rood maken###############################################################
    layer = iface.activeLayer()

    layer.startEditing()

    for feature in layer.getFeatures():
        if feature ['NUMPOINTS2'] ==0:
            layer.changeAttributeValue(feature.id(), layer.fields().indexFromName('kleur'),'blue')
        else:
           layer.changeAttributeValue(feature.id(), layer.fields().indexFromName('kleur'),'red') 
    layer.commitChanges()



    # rood en blauw samenvoegen##################################################################
    CombineDots = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/CombineDots"+str(N)+".shp"

    processing.run("native:mergevectorlayers", 
    {'LAYERS': [NewDots,RedDots],'CRS':None,'OUTPUT':CombineDots})

    iface.addVectorLayer(CombineDots,'','ogr')

    #kleur aanpassen##################################################################3
    layer = iface.activeLayer()

    # define some rules: label, expression, color name, (min scale, max scale)
    road_rules = (
        ('rood', "kleur ='red'", 'red', None),
        ('blauw', "kleur ='blue'",'blue', None)
    )

    # create a new rule-based renderer
    symbol = QgsSymbol.defaultSymbol(layer.geometryType())
    renderer = QgsRuleBasedRenderer(symbol)

    # get the "root" rule
    root_rule = renderer.rootRule()

    for label, expression, color_name, scale in road_rules:
        # create a clone (i.e. a copy) of the default rule
        rule = root_rule.children()[0].clone()
        # set the label, expression and color
        rule.setLabel(label)
        rule.setFilterExpression(expression)
        rule.symbol().setColor(QColor(color_name))
        # set the scale limits if they have been specified
        if scale is not None:
            rule.setScaleMinDenom(scale[0])
            rule.setScaleMaxDenom(scale[1])
        # append the rule to the list of rules
        root_rule.appendChild(rule)

    # delete the default rule
    root_rule.removeChildAt(0)

    # apply the renderer to the layer
    layer.setRenderer(renderer)


    #laag verwijderen#########################################################################
    TempLayer1 = QgsProject.instance().mapLayersByName('NewDots'+str(N))[0].id()
    if (N==0):
        TempLayer2 = QgsProject.instance().mapLayersByName('PDots')[0].id()
    else:
        None
        ### vorige verwijderen############ 
        #Templayer3=QgsProject.instance().mapLayersByName('CombineDots'+str(N))[0].id()
        #QgsProject.instance().removeMapLayers([TempLayer3])
    
    
    QgsProject.instance().removeMapLayers( [TempLayer1] )
    #QgsProject.instance().removeMapLayers( [TempLayer2] )
   
    
#############################################################################################
    N =N+ 1
    
    input = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/CombineDots"+str(N)+".shp"
    
else:
    print(str(N)+"x doorlopen")
i=0
while (i<(N-1)):
    TempLayerX = QgsProject.instance().mapLayersByName('CombineDots'+str(i))[0].id()
    QgsProject.instance().removeMapLayers( [TempLayerX] )
    TempLayerX = QgsProject.instance().mapLayersByName('CombineDots'+str(i))[0].id()
    QgsProject.instance().removeMapLayers( [TempLayerX] )
    i = i+1
else:
    t_eind = time.localtime()
    print(time.strftime('%H:%M:%S', t_eind))



import processing
import os
import shutil
import time

t_begin = time.localtime()
print(time.strftime('%H:%M:%S', t_begin))

input = 'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/PDots.shp'
N=0


while(N<10):
    print("N="+str(N))
    outFile = 'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/temp_buffer'+str(N)+'.shp'
    layer = iface.addVectorLayer(input,'','ogr')
   # geselecteerd1 = layer.selectByExpression("kleur = 'blue'")
    geselecteerd1= layer.selectByExpression("kleur = 'blue'")
    #puntlaag voor buffer maken########################################################
    BufferFile = 'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/buffer'+str(N)+'.shp'
    #print(BufferFile)

    writer = QgsVectorFileWriter.writeAsVectorFormat(layer,BufferFile,'utf-8',
    driverName = 'ESRI Shapefile', onlySelected= True)

    #selected_layer1 = iface.addVectorLayer(BufferFile,'','ogr')
    del(writer)

    #buffer maken met puntlaag "BufferFile"###########################################
    processing.run("native:buffer", {'INPUT':'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/buffer'+str(N)+'.shp',
    'DISTANCE':30,'SEGMENTS':5,'END_CAP_STYLE':0,'JOIN_STYLE':0,
    'MITER_LIMIT':2,'DISSOLVE':False,
    'OUTPUT':outFile})

    #iface.addVectorLayer(outFile,'','ogr') #voeg bufferlaag toe aan kaart

    layer.removeSelection()
    geselecteerd2 = layer.selectByExpression("kleur = 'red'")

    #puntlaag maken van rode punten####################################################
    RedDots = 'C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/RedDots'+str(N)+'.shp'
    writer = QgsVectorFileWriter.writeAsVectorFormat(layer,RedDots,'utf-8',
    driverName = 'ESRI Shapefile', onlySelected= True)

    #selected_layer2 = iface.addVectorLayer(RedDots,'','ogr')
    del(writer)

    #layer.removeSelection()

    #rode punten in buffer tellen#######################################################
    CountFile = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/temp_count"+str(N)+".shp"
    if (N==2):
        processing.run("native:createspatialindex", {'INPUT':RedDots})
    else:
        processing.run("native:createspatialindex", {'INPUT':RedDots})

    processing.run("native:countpointsinpolygon",{
    'POLYGONS':outFile,
    'POINTS':RedDots,
    'WEIGHT':'','CLASSFIELD':'','FIELD':'NUMPOINTS2',
    'OUTPUT':CountFile})

    #iface.addVectorLayer(CountFile,'','ogr')

    #punten maken van polygoon punten tellen################################################
    NewDots = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/NewDots"+str(N)+".shp"
    processing.run("native:centroids", 
    {'INPUT': CountFile,'ALL_PARTS':True,'OUTPUT':NewDots})

    iface.addVectorLayer(NewDots,'','ogr')

    # blauw naar rood maken###############################################################
    layer = iface.activeLayer()

    layer.startEditing()

    for feature in layer.getFeatures():
        if feature ['NUMPOINTS2'] ==0:
            layer.changeAttributeValue(feature.id(), layer.fields().indexFromName('kleur'),'blue')
        else:
           layer.changeAttributeValue(feature.id(), layer.fields().indexFromName('kleur'),'red') 
    layer.commitChanges()



    # rood en blauw samenvoegen##################################################################
    CombineDots = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/CombineDots"+str(N)+".shp"

    processing.run("native:mergevectorlayers", 
    {'LAYERS': [NewDots,RedDots],'CRS':None,'OUTPUT':CombineDots})

    iface.addVectorLayer(CombineDots,'','ogr')

    #kleur aanpassen##################################################################3
    layer = iface.activeLayer()

    # define some rules: label, expression, color name, (min scale, max scale)
    road_rules = (
        ('rood', "kleur ='red'", 'red', None),
        ('blauw', "kleur ='blue'",'blue', None)
    )

    # create a new rule-based renderer
    symbol = QgsSymbol.defaultSymbol(layer.geometryType())
    renderer = QgsRuleBasedRenderer(symbol)

    # get the "root" rule
    root_rule = renderer.rootRule()

    for label, expression, color_name, scale in road_rules:
        # create a clone (i.e. a copy) of the default rule
        rule = root_rule.children()[0].clone()
        # set the label, expression and color
        rule.setLabel(label)
        rule.setFilterExpression(expression)
        rule.symbol().setColor(QColor(color_name))
        # set the scale limits if they have been specified
        if scale is not None:
            rule.setScaleMinDenom(scale[0])
            rule.setScaleMaxDenom(scale[1])
        # append the rule to the list of rules
        root_rule.appendChild(rule)

    # delete the default rule
    root_rule.removeChildAt(0)

    # apply the renderer to the layer
    layer.setRenderer(renderer)


    #laag verwijderen#########################################################################
    TempLayer1 = QgsProject.instance().mapLayersByName('NewDots'+str(N))[0].id()
    if (N==0):
        TempLayer2 = QgsProject.instance().mapLayersByName('PDots')[0].id()
    else:
        None
        ### vorige verwijderen############ 
        #Templayer3=QgsProject.instance().mapLayersByName('CombineDots'+str(N))[0].id()
        #QgsProject.instance().removeMapLayers([TempLayer3])
    
    
    QgsProject.instance().removeMapLayers( [TempLayer1] )
    #QgsProject.instance().removeMapLayers( [TempLayer2] )
   
    
#############################################################################################
    N =N+ 1
    
    input = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/CombineDots"+str(N)+".shp"
    
else:
    print(str(N)+"x doorlopen")
i=0
while (i<(N-1)):
    TempLayerX = QgsProject.instance().mapLayersByName('CombineDots'+str(i))[0].id()
    QgsProject.instance().removeMapLayers( [TempLayerX] )
    TempLayerX = QgsProject.instance().mapLayersByName('CombineDots'+str(i))[0].id()
    QgsProject.instance().removeMapLayers( [TempLayerX] )
    i = i+1
else:
    t_eind = time.localtime()
    print(time.strftime('%H:%M:%S', t_eind))

Answer 1

You must increase variable N after assigning a value to variable input. Because the assigned value of input contains N. If you increase N before input line, you assign a non-existent file to variable input.

Replace two lines below:

From

N = N + 1

input = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/CombineDots"+str(N)+".shp"

To

input = "C:/Users/laptop Innoforte 1/Innoforte/Innoforte Druten - Documenten/1. projecten/2. status uitvoering/GOV duurzame energiesystemen/3. rekenmodellen/QGIS/QGIS template/CombineDots"+str(N)+".shp"

N = N + 1