avoid on duplicate user functions (fixes #13579)

jef-n · jef-n · commit e7a981cc9565 · 2015-11-26T20:32:29.000+01:00
(backports from commit cc9c789)
diff --git a/python/core/__init__.py b/python/core/__init__.py
@@ -1,6 +1,7 @@
 import inspect
 import string
 from qgis._core import *
+from PyQt4.QtCore import QCoreApplication
 
 def register_function(function, arg_count, group, usesgeometry=False, **kwargs):
     """
@@ -66,7 +67,10 @@ def func(self, values, feature, parent):
     register = kwargs.get('register', True)
     if register and QgsExpression.isFunctionName(name):
         if not QgsExpression.unregisterFunction(name):
-            raise TypeError("Unable to unregister function")
+            msgtitle = QCoreApplication.translate("UserExpressions", "User expressions")
+            msg = QCoreApplication.translate("UserExpressions", "The user expression {0} already exists and could not be unregistered.").format(name)
+            QgsMessageLog.logMessage(msg + "\n", msgtitle, QgsMessageLog.WARNING)
+            return None
 
     function.__name__ = name
     helptext = helptemplate.safe_substitute(name=name, doc=helptext)
