[GIS] How to write log message in QGIS’s script algorithms GUI tab

logpyqgisqgis-processing

I want to write some log in the log tab of processing algorithm User Interface.

I tried this :

from qgis.core import QgsMessageLog

QgsMessageLog.logMessage("test")

but when I launch the script "test" is not logged.

How to write a log in the processing User Interface ?

the processing guide log's chapter doesn't tell much about writing a log in this tab.

If i use :

from qgis.core import QgsMessageLog
QgsMessageLog.logMessage("test", tag="Processing", level=QgsMessageLog.INFO)

the log result is wrote under the console log panel called "Processing", but not in the processing GUI log tab.

Best Answer

For QGIS 3.x you can use the pushInfo() method on a feedback object:

feedback.pushInfo('This is a log message')

See the scripts section of the user's manual for other relevant methods.

Related Solutions

PyQGIS – Importance of Import Order in Standalone Processing Scripts

tl;dr

import qgis
import PyQt4
etc

is the correct way

Long version

Yes the import order can matter and in the case of QGIS 2.0 and above it does matter.

You should always import qgis.core or qgis.gui, even just import qgis is enough, before you import any PyQt stuff.

That seems silly. Why?

In QGIS 2.0 we switched to using version 2 bindings of SIP which made API calls more Python like e.g it will auto convert types for you:

1.0 SIP you had to do:

value.toString()

in 2.0

value

will just work if it's a string type in the C++ code.

Ok So what

The kicker is that we have to set the API version to 2 in code before it gets set my something else, you can't set it again once it's been set. If you import PyQt first it will set the value to v1 but everything in QGIS now uses v2. In order to fix this we set it to v2 in qgis.__init__.py but we have to import qgis first or else PyQt wins.

Because all of the plugins in QGIS 2.0 and above now use SIP v2 any SIP v1 like calls will generate a error when running.

PyQGIS – Getting Log Messages from QGIS Processing Framework

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())

Best Answer

Related Solutions

PyQGIS – Importance of Import Order in Standalone Processing Scripts

PyQGIS – Getting Log Messages from QGIS Processing Framework

Related Question