1

Related to Import error for qgis.core when running OSGeo4w shell script

I try to detect if my script is run from a QGIS instance (through the plugin) or from a standard python console. This detection will enable conditional imports of the required librairies which are different from a case to the other.

For conditional imports, I found here

try:
    import module
except ImportError:
    import otherModule as module

and tried to adapt it for my use case but I can't raise a convenient error:

E.G.

try:
    import processing

except:
    # Load required libraries to run from python (!Unstable!)
    # See https://gis.stackexchange.com/questions/129915/cannot-run-standalone-qgis-script
    # for any improvements
    import os, sys, glob

    # Prepare the environment
    ... 
    # See https://gis.stackexchange.com/questions/129915/cannot-run-standalone-qgis-script

Returns me following error : QPixmap: Must construct a QApplication before a QPaintDevice

and does not instead enters the except clause what is sad.

2

The error QPixmap: Must construct a QApplication before a QPaintDevice seems to be related to the fact you don't declare a QApplication before your try/except statement.

The other issue about try except is only about Python.

You can manage error correctly with:

try:
    # To be sure it fails
    import processing1
except Exception, e:
    print type(e), e

You will see that you can catch various exceptions types. There is one specific import error. Hence, above try/except could be improve with:

try:
    # To be sure it fails
    import processing1
except ImportError, e:
    print type(e), e
else:
    print "Other error"

Edit: Although my answer was correct, it wasn't enough to help.

You can do the following to differentiate context:

try:
    canvas = iface.mapCanvas()
    print 'You are in a QGIS console'
except Exception, e:
    print 'You are in an external script', e

iface is imported only in a QGIS console context e.g the official docs http://docs.qgis.org/testing/en/docs/pyqgis_developer_cookbook/intro.html#python-console

  • The goal is to detect if we are on Qgis console or on an extern python console (because imports are different). That's why I tried to generate an error. But the "QPixmap: Must construct a QApplication before a QPaintDevice" makes the console crash and the error handling does not goes through the except clause as it should in a good error management system. – Nono Jan 21 '16 at 22:55
  • Great, ty for the edit! I went other the docs, but not carefully enough! – Nono Jan 22 '16 at 12:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.