Encountering this weird bug. I'm using QGIS 3.4.7. I am trying to write a script but it crashes when I run it from the editor. But it does not crash when run from the Processing Toolbox. Right now the script does not do anything yet. It just takes an input and outputs it.

Sometimes, instead of crashing, I get this Python error

Traceback (most recent call last):
File "C:/OSGEO4~1/apps/qgis-ltr/./python/plugins\processing\gui\AlgorithmDialog.py", line 247, in on_complete
self.feedback.pushInfo(self.tr('Execution completed in {0:0.2f} seconds').format(time.time() - start_time))
NameError: free variable 'self' referenced before assignment in enclosing scope

Edited to include code. I didn't include it before because the code is just a copy of the template and it just outputs the same input layer.

def processAlgorithm(self, parameters, context, feedback):
    lpi_lyr = self.parameterAsSource(
    if lpi_lyr is None:
        raise QgsProcessingException(self.invalidSourceError(parameters, self.INPUT))

    feedback.pushInfo('CRS is {}'.format(lpi_lyr.sourceCrs().authid()))

    count = lpi_lyr.featureCount()
    total = 100.0 / count if count else 0

    feats = [feat for feat in lpi_lyr.getFeatures()]
    feedback.pushInfo('Total number of features: {}'.format(len(feats)))     

    mem_lyr = QgsVectorLayer("Point?crs="+lpi_lyr.sourceCrs().authid(), 'point', 'memory') 
    prov = mem_lyr.dataProvider()
    prov.addAttributes([field for field in lpi_lyr.fields()]) 

    output_lyr = lpi_lyr
    (sink, dest_id) = self.parameterAsSink(

    if sink is None:
        raise QgsProcessingException(self.invalidSinkError(parameters, self.OUTPUT))           

    features = output_lyr.getFeatures()

    for current, feature in enumerate(features):
        # Stop the algorithm if cancel button has been clicked
        if feedback.isCanceled():
        # Add a feature in the sink
        sink.addFeature(feature, QgsFeatureSink.FastInsert)
        # Update the progress bar
        feedback.setProgress(int(current * total))  

    feedback.pushInfo('Finished writing sink')

    return {self.OUTPUT: dest_id}
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  • I've had similar problems and I'm not sure if it's related to context/feedback parameters as reported elsewhere as a lot of my scripts don't use native algorithms. I think it's the way QGIS scripts handle the compiling when saving the scripts. I suspect that hitting the save button in the editor window it saves a pyc compiled version of the script and when running the tool again with the play button it gets confused with which one to use. If you close the editor and run from the processing toolbox, no crashes at all. Conversely live arcpy script edits have no such problems. – GIS_py Nov 25 '19 at 10:07

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