Converting PyQt5.QtCore.QVariant to string

Question

I am using QGIS with the in-built Python console. I want to replace some values in a shapefile with some other values. But when I try to change the attribute values, I get an error about the data types (see the code below):

Error: AttributeError: 'QVariant' object has no attribute 'split'

However, I find no way to convert the QVariant to a String. If I run the code without the editing turned on, everything works fine, but the changes are not saved. How can I convert the QVariant to a string and are there ways around this issue?

shp_layer = QgsVectorLayer(shp_path, "", "ogr")

with edit(shp_layer):
    for feature in shp_layer.getFeatures():
        height_str_list = feature[height_list_field].split(":", 1)[1][:-1].split(",")  # some fancy string editing in here, but i swear it works
        if '...' in height_str_list:
            height_str_list.remove('...')
        height_flt_list = [float(i) for i in height_str_list]
        feature[height_field] = sum(height_flt_list)/len(height_flt_list)  # because QGIS pretends not to know mean()
        shp_layer.updateFeature(feature)
    shp_layer.setSubsetString("")

I also discovered if I say height_str_list = feature[height_list_field].value().split(....)

I get another error:

"AttributeError: 'str' object has no attribute 'value'"

Answer 1

A perfect comment from @Jochen Schwarze:

When I do a=QVariant(42), str(a) I get something like '<PyQt5.QtCore.QVariant object at 0x00000274E6B760B8>' and not '42'

because just with the str() you may not get the desired output.

>>> a = QVariant(42)
>>> str(a)
'<PyQt5.QtCore.QVariant object at 0x000001700D003BA0>'

As a workaround to that issue I may suggest this solution:

Using the value() method

>>> a = QVariant(42)
>>> str(a.value())
'42'
>>> type(str(a.value()))
<class 'str'>

If you know that you have a string inside of your QVariant class, you can additionally use convert(*int targetTypeId*)-method, 'targetTypeId' is possible to find here, in our case it is 10.

>>> a = QVariant(42)
>>> a.convert(10)
True
>>> a.value()
'42'
>>> type(a.value())
<class 'str'>

Answer 2

The solution is to use str() on the QVariant.