"AttributeError: 'dict' object has no attribute 'fields'" error when creating and deleting fields in the attribute table using PyQGIS

Question

I am currently making a code that will buffer the points then extract vertices and add new coordinates. but I also want to change the "max depth" column to "Height Theo" and then add another column called "Height actual" and the values below it should be equal to the negative (-) value of "Height Theo" before exporting this to CSV file.

This is the output of my current script:

enter image description here

This is the output I want.

enter image description here

This is my code:

from qgis import processing
from datetime import datetime, timedelta
view = iface.layerTreeView()
selected_nodes = view.selectedNodes()
selected_layers = [node.layer() for node in selected_nodes]
print("merging layers....")
merge = processing.runAndLoadResults("native:mergevectorlayers", {
 'LAYERS': selected_layers,
 'CRS': QgsCoordinateReferenceSystem('USER:100000'),
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })
print('Creating Buffer...')
buffer = processing.runAndLoadResults("native:buffer", {
 'INPUT': merge['OUTPUT'],
 'DISTANCE': 0.18,
 'SEGMENTS': 2,
 'END_CAP_STYLE': 0,
 'JOIN_STYLE': 0,
 'MITER_LIMIT': 2,
 'DISSOLVE': False,
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })
 
print('extracting points...')
vertices = processing.runAndLoadResults("native:extractvertices", {
 'INPUT': buffer['OUTPUT'],
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })
print('adding xycoords...')
xycoords = processing.runAndLoadResults("qgis:exportaddgeometrycolumns", {
 'INPUT': vertices['OUTPUT'],
 'CALC_METHOD': 0,
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })
dont_delete = ["ID", "X [m]", "Y [m]", "Max. depth [m]"]
all_fields = xycoords.fields().names()
field_ids = [xycoords.fields().indexFromName(f) for f in all_fields if f not in dont_delete]
xycoords.dataProvider().deleteAttributes(field_ids)
xycoords.updateFields()

deleting fields does not work

# Python Console
# Use iface to access QGIS API interface or type help(iface) for more info
# Security warning: typing commands from an untrusted source can harm your computer
exec(Path('C:/Users/CMCA/OneDrive - Boskalis/Documents/Trial PyQGIS/Creating_Grab.py').read_text())
merging layers....
Creating Buffer...
extracting points...
adding xycoords...
Traceback (most recent call last):
 File "C:\PROGRA~1\QGIS33~1.0\apps\Python39\lib\code.py", line 90, in runcode
 exec(code, self.locals)
 File "<input>", line 1, in <module>
 File "<string>", line 83, in <module>
AttributeError: 'dict' object has no attribute 'fields'

Answer 1

I could get the same error:

Traceback (most recent call last):
 File "C:\PROGRA~1\QGIS32~1.0\apps\Python39\lib\code.py", line 90, in runcode
 exec(code, self.locals)
 File "<input>", line 1, in <module>
 File "<string>", line 10, in <module>
AttributeError: 'dict' object has no attribute 'fields'

AttributeError arose due to the output type of the "qgis:exportaddgeometrycolumns" algorithm:

{'OUTPUT': <QgsVectorLayer: 'Added geom info' (memory)>}

As you can see it is a dictionary, however, to achieve field names, one needs to treat the QgsVectorLayer only. This can be done by adding the ['OUTPUT'] into your code.

So, please edit your code:

xycoords = processing.runAndLoadResults("qgis:exportaddgeometrycolumns", {
 'INPUT': vertices['OUTPUT'],
 'CALC_METHOD': 0,
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })

as follows:

xycoords = processing.runAndLoadResults("qgis:exportaddgeometrycolumns", {
 'INPUT': vertices['OUTPUT'],
 'CALC_METHOD': 0,
 'OUTPUT': 'TEMPORARY_OUTPUT'
 })['OUTPUT']

Then I can easily get field names of the xycoords temporary layer with:

all_fields = xycoords.fields().names()