Delete fields/attributes from QgsVectorLayer (PyQGIS)

Question

UPDATE 2 Again I updated the code according to this: https://docs.qgis.org/3.28/en/docs/pyqgis_developer_cookbook/vector.html#modifying-vector-layers-with-an-editing-buffer. But now I have a again the problem, that no field is deleted. My code:

            dlayer = QgsVectorLayer(filename, 'layer_name', 'ogr')
            fieldnames = [field.name() for field in dlayer.fields()]
            print(len(fieldnames))
            dlayer.startEditing()
            dlayer.deleteAttributes([1])
            dlayer.commitChanges()
            fieldnamesUpdated = [field.name() for field in dlayer.fields()]
            print(len(fieldnamesUpdated))

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UPDATE I updated the code according to the suggestions, but I still get the assertion error. This is the error: File "C:\PROGRA~1\QGIS32~1.3\apps\qgis\python\qgis\core\additions\edit.py", line 38, in __enter__ assert self.layer.startEditing() AssertionError.

This is my code now, what am I still doing wrong?

def deleteFields(path):
    xml_list_paths = []
for file in os.listdir(path):
    # make sure to only get the files with certain type, e.g. '.shp'
    if 'xml' in file:
        filename = f'{path}\{file}'
        # print(filename)
        xml_list_paths.append(filename)

        dlayer = QgsVectorLayer(filename, 'layer_name', 'ogr')

        # Create a list of the fieldnames you want to delete:
        fieldnames_to_delete = [field.name() for field in dlayer.fields()]
        # Enter Edit mode
        with edit(dlayer):
            # Create empty list we will fill with the fieldindexes
            fields_to_delete = []
            # Iterate over the list of fieldnames and get the indexes
            for fieldname_to_delete in fieldnames_to_delete:
                # Get the field index by its name:
                fieldindex_to_delete = dlayer.fields().indexFromName(fieldname_to_delete)
                # You can also check if the field exists
                if fieldindex_to_delete == -1:
                    # If it does not exist, just skip it and go to the next one. This may prevent a crash or error :)
                    continue
                # Append the index to the list
                fields_to_delete.append(fieldindex_to_delete)
            # Delete the fields by their indexes, note that it has to be a list:
            dlayer.dataProvider().deleteAttributes(fields_to_delete)
        # Update the fields, so the changes are recognized:
        dlayer.updateFields()

---

---

I have multiple (~4000) xml-files, which I want to merge. As I stumpled about a length-problem of a certain field, when trying to merge, and I only need the geometry of the objects, I would like to first remove all the attributes (or 'fields') from the files.

I tried to create script which should delete a field (as an example) but it seems to do literally nothing:

def mergeXMLFiles(path):
for file in os.listdir(path):

    if 'xml' in file:
        filename = f'{path}\{file}'



        # create Qgis-Vector layer 
        dlayer = QgsVectorLayer(filename, 'layer_name', 'ogr')

        # Create list from all field names and count 
        listoffields = [field.name() for field in dlayer.fields()]
        print(len(listoffields))

        # Delete the field with index 1 as an Example
        # and update the fields
        dlayer.dataProvider().deleteAttributes([1])
        dlayer.updateFields()

        # Create again a list of all fields in the layer and print
        # the count of the field names
        updatedlistoffields = [field.name() for field in dlayer.fields()]
        print(len(updatedlistoffields))

The second list should have less fields than the first list, but it doesn't, so I guess the deletion , so the code

            dlayer.dataProvider().deleteAttributes([1])
            dlayer.updateFields()

doesnt delete the field with index 1. What am I doing wrong?