I have a line layer with lines potentially having multiple vertices (aside from start and end point) and I need the concerned features to be split at the vertex.

The explodelines algorithm does this but it creates a new layer. I need imperatively to edit my input layer as opposed to create a new one. I can't also create a new .shp layer and work with that one instead since I need to run a bunch of operations on it.

So far I've found these two threads Building a QGIS 3.10 script without an output layer and Modify the input layer when using processing algorithms from the console but I can't find a solution in neither.

If there's somehow a way to directly edit input layer directly using processing algorithms that would be the best case scenario as a lot of operations are covered by readily available algorithms already.

2 Answers 2


You can run Processing algorithms to edit input features in-place (that is, to modify the INPUT layer instead of modifying a copy) in this way:

from processing.gui.AlgorithmExecutor import execute_in_place

# Get algorithm instance
registry = QgsApplication.instance().processingRegistry()
alg = registry.algorithmById("native:explodelines")

# Run the algorithm using 'in-place' edits
line_layer = iface.activeLayer()
params = {'INPUT': line_layer}
execute_in_place(alg, params)


  • It is not required that your INPUT layer is the current active layer. Just pass a reference to a layer and you're done.
  • Make sure you don't have any feature selection on your input layer before running the algorithm. Otherwise, changes will only be applied to selected features.
  • After the algorithm execution, your layer will be in edit mode waiting for you to save changes (just like when you run it from the GUI). As you're using a script, it makes sense to save changes also automatically. For that, just write line_layer.commitChanges() at the end.
  • The native:explodelines only expects the INPUT/OUTPUT layer parameters. For other algorithms, you'd pass the whole set of parameters (see how to get parameters of a specific algorithm).
  • There is no need of passing the OUTPUT parameter to run an algorithm in-place, but if you pass it, the algorithm will still work in-place mode.
  • It may be useful to check if an algorithm can be run in-place on a specific layer, before running it. For that, you can use alg.supportInPlaceEdit(line_layer), which returns a boolean result.

Some of the processing scripts you can use "in place" just press the inplace button. Explode lines is one of them. There will no new layer produced.

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  • Hi, thanks for the quick response. I can get snap geometries to layer i.sstatic.net/scfP6.png but I don't get it for explode lines i.sstatic.net/vURTF.png Also, would there a way to do it through a python script as opposed to running it from the processing toolbox ? Commented Sep 20, 2021 at 10:48
  • While running the snap geometries to layer algorithm while "Edit features in palce" enabled, the "source layer" argument is missing, so I can only the reference layer so I can't pick the point layer which it should snap to. @eurojam Commented Sep 20, 2021 at 10:56
  • you have to select the layer before searching explode, if your active layer will be a pointlayer, there will no explode
    – eurojam
    Commented Sep 20, 2021 at 11:08
  • Great @eurojam - did not know about this possibility!
    – Babel
    Commented Sep 20, 2021 at 12:05

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