Getting log message from QGIS processing framework?

Question

I run Python processing algorithms externally, and I want to get the log output I see when I run it from the QGIS 3 GUI at the log tab as shown in the screenshot:

enter image description here

I want to get the full grey log output when Result is returned only.

How do I do that?

An example follows:

import os
import sys
import gdal
gdal.UseExceptions() # Allow GDAL to throw Python Exceptions
from qgis.core import (
 QgsApplication,
 QgsProcessingFeedback,
 QgsMessageLog)
from qgis.analysis import QgsNativeAlgorithms
QgsApplication.setPrefixPath(os.path.join("C:", os.sep, "OSGeo4W64", "apps", "qgis"), True)
qgs = QgsApplication([], False)
qgs.initQgis()
sys.path.append(os.path.join("C:", os.sep, "OSGeo4W64", "apps", "qgis", "python", "plugins"))
import processing
from processing.core.Processing import Processing
Processing.initialize()
QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())
def pca(input_raster_list):
 params = {
 'input': input_raster_list,
 'rescale': [0,0],
 'percent': 99,
 '-n': True,
 '-f': False,
 'output': 'C:\\Users\\...',
 'GRASS_REGION_PARAMETER': None,
 'GRASS_REGION_CELLSIZE_PARAMETER': 0
 }
 feedback = QgsProcessingFeedback()
 res = processing.run("grass7:i.pca", params, feedback=feedback)
 print(res)
 return

• ndawson: Can you post a small code sample showing how you are calling the algorithms?
• ODstuck: Can the question be reopened now that more detail and specifications are included? It was supposed to be a generic question on how to get the logs from QGIS, but maybe now it is more clear.
• PolyGeo: Even "generic" questions about code should always include a code snippet that illustrates what you have tried and where you are stuck.

Answer 1

You can subclass QgsProcessingFeedback to implement your own custom logging logic. E.g.

class MyFeedBack(QgsProcessingFeedback):
 def setProgressText(self, text):
 print(text)
 def pushInfo(self, info):
 print(info)
 def pushCommandInfo(self, info):
 print(info)
 def pushDebugInfo(self, info):
 print(info)
 def pushConsoleInfo(self, info):
 print(info)
 def reportError(self, error, fatalError=False):
 print(error)

This one will just print everything to the console, but you could modify the logic to write to a file, etc.

Then, whenever you call processing.run, make sure you pass an instance of your subclass as the feedback argument:

res = processing.run("grass7:i.pca", params, feedback=MyFeedBack())

• ODstuck: Thank you once more Nyall! You are right that code is needed and necessary for any help. The solution is helpful and insightful.