Using processing algorithm in QGIS plugin

Question

I'm building a plugin in QGIS, one of its part is processing algorithm: intersection. I want to save the result as memory layer, and then work on it. Following code was working fine, nothing changed (I changed nothing), and: boom! it stopped working. The problem is in the 2nd line:

processing.runandload("qgis:intersection",selectedLayer,selectedLayer_2, "memory:temp_layer")
layer = QgsMapLayerRegistry.instance().mapLayersByName("memory:temp_layer")[0]

The memory layer is created (I can see it in QGIS) but I can't define 'layer'. I'm getting an error:

IndexError: list index out of range.

Why? :(

• antonio: Ok, that's weird... Plugin works on different computer. I tested it on 4 computers, it was working on 2 of them, on the other 2 there was the same error.
• SIGIS: From where do you launch your code (inside Qgis or outside) (in the python Qgis console)?
• antonio: I edit the mainplugin.py code in code editor, save edits, reload plugin with reloader. So I guess the correct answer is that I launch it from outside.

Answer 1

I suspect this is probably dependent on the Processing plugin version for each of those computers. Your following line checks the list of loaded layers and will only define layer if a layer has the name memory:temp_layer.

layer = QgsMapLayerRegistry.instance().mapLayersByName("memory:temp_layer")[0]

In the older versions of the Processing plugin, you can define the name of the memory layer "memory:any_name". The line above will work.

In the latest versions, the default name of the tool is used instead (e.g. "Intersection"). The line above will not work.

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I would suggest checking the Processing plugin for each of your computers and updating it to the latest version (currently at 2.12.2) from the toolbar:

Plugins> Manage and Install Plugins...

And use the following line instead:

layer = QgsMapLayerRegistry.instance().mapLayersByName("Intersection")[0]

• antonio: Thanks. I checked the version of Processing plugin and it was 2.12.99 while 'the available version is 2.12.2'. The information in plugin manager was: 'Installed version is NEWER than version available in official repository.' Well, that's interesting.I also did recommended changes in code and it works.
• Joseph: @antonio - Haha that is interesting! Weird little glitch I guess but glad you got it working =)