Returning error text from QgsProcessingFeedback

Question

I have a snippet that intersects two map layers (blockLayer and ogLayer) in QGIS; and prints out when a bad geometry prevents the intersection from occurring. It builds a subclass from QgsProcessingFeedback, based on the answer posted here by @ndawson.

Here's the code:

class MyFeedBack(QgsProcessingFeedback): # create a subclass from the QgsProcessingFeedback class
 def reportError(self, error, fatalError=False): # QgsProcessingFeedback.reportError() is a method 
 if "invalid geometry" in error:
 featNum = error.split("(")[1].split(")")[0]
 print("{} has bad geometry".format(featNum))
 
blockLayer = QgsProject.instance().mapLayersByName("harvestApprovals")[0]
ogLayer = QgsProject.instance().mapLayersByName('Boundary old growth .gdb layer')[0]
#feedback = QgsProcessingFeedback.reportError(self, error, fatalError=False)
#feedback = QgsProcessingFeedback.reportError(error, fatalError=False)
feedback = QgsProcessingFeedback() # instantitate the QgsProcessingFeedback class
print(feedback)
params = {'INPUT':blockLayer,'OVERLAY':ogLayer,'OUTPUT':'TEMPORARY_OUTPUT'}
rslt = processing.run("native:intersection", params, feedback=MyFeedBack())
print("\nDone!")

I'd prefer to create a list to add those numbers to, so as to know which geometries need repair. I'm just not sure how (or if it's possible) to build a list within an instance of a class, and somehow return that list from the class.

Is there some way I could myList.append(featNum) as the errors are encountered, then get myList back after the process has run?

Answer 1

When I run your script, print statement never run although I get an error. Thus, I couldn't test it. But the following way should work for you.

• Add a variable (myList = []) to root scope.
• Use it in reportError method with global keyword.

myList = []
class MyFeedBack(QgsProcessingFeedback): 
 def reportError(self, error, fatalError=False): 
 if "invalid geometry" in error:
 featNum = error.split("(")[1].split(")")[0]
 global myList
 myList.append(featNum)
#
# other lines
#
print(myList)
print("\nDone!")