Iterating over map layers using PyQGIS

Question

I'm having trouble figuring out how to iterate over map layers. I can access the currently highlighted layer in the table of contents via iface.activeLayer() but I want my code to operate on all layers.

I don't see anything in the API that provides easy access to this functionality and couldn't find a good online example but maybe I missed something?

Answer 1

Try...

# substitute 'self' with 'qgis.utils.iface' when run from Python console
# 'self.iface = iface' would usually precede this command in your class 
layers = self.iface.legendInterface().layers()

for layer in layers:
    layerType = layer.type()
    if layerType == QgsMapLayer.VectorLayer:
        # do some stuff here

Culled from consolidatethread.py from QConsolidate plugin.

Description of QgsLegendInterface object returned from legendInterface().

Edit: added info on 'self' above.

Answer 2

For QGIS 3, QgsMapLayerRegistry's functionality has been moved to QgsProject.

So, for iterating over map layers, you should use that structure:

layers = QgsProject.instance().mapLayers()

.mapLayers() returns a dictionary structured as {layer_x_id: layer_x, layer_y_id: layer_y, ....}. Then you can iterate over layers like:

for layer_id, layer in layers.items():
    print(layer.name())

Because .mapLayers() returns a dictionary (dict), you can also use .values() method of dictionary which returns just a list which contains layers in that case. Then you can iterate over layers like:

layers = QgsProject.instance().mapLayers().values()

for layer in layers:
    print(layer.name())

---

If you prefer, you can iterate in this way:

layers = QgsProject.instance().mapLayers() # dictionary

for layer in layers.values():
    print(layer.name())

Answer 3

There are also two other ways:

layers = self.iface.mapCanvas().layers()

will give you a list of layers

or

layers = QgsMapLayerRegistry.instance().mapLayers()

for name, layer in layers.iteritems():
     print name, layer.type()

Answer 4

For QGIS 2.6 here is the code to identify each layer and group them:

#make the desired groups for layers
toc = self.iface.legendInterface()
root = QgsProject.instance().layerTreeRoot()
group1 = root.insertGroup(0, "Group Point")
group2 = root.insertGroup(1, "Group Line")
group3 = root.insertGroup(2, "Group Polygon")
#get the list of layers  from registry
layers = QgsMapLayerRegistry.instance().mapLayers()
#segregate layers into groups 
for name, layer in layers.iteritems():
    # check the layer geometry type 
    if layer.geometryType() == QGis.Point:
        toc.moveLayer(layer, 0)

    if layer.geometryType() == QGis.Line:
        toc.moveLayer(layer, 1)

    if layer.geometryType() == QGis.Polygon:
        toc.moveLayer(layer, 2)

Note: After grouping I have to remove the duplicate layer so I used root.removeLayer(lyr).

Answer 5

Visible layers

You can iterate visible layers in this way:

# Iterate visible layers (warning: only spatial ones)
def iterate_visible_layers():
    for layer in iface.mapCanvas().layers():
        # TODO: Do something interesting with the layers
        print(layer.name())
    
iterate_visible_layers()

Layers in TOC (layers panel / legend / layer tree)

In case that you need all layers in the TOC/Layers-panel (not only those that are visible/checked, as mapCanvas().layers() returns), you can use this function:

# Iterate all ToC layers (warning: only spatial ones)
def iterate_toc_layers(group):
    for tree_layer in group.findLayers():
        # TODO: Do something interesting with the layers
        print(tree_layer.layer().name())

root = QgsProject.instance().layerTreeRoot()
iterate_toc_layers(root)

Note: You can iterate layers from a specific group by passing such a group to iterate_toc_layers(), in this way:

my_group = root.findGroup('My group')
iterate_toc_layers(my_group)

All registered layers

QGIS can use layers that are part of the QGIS project but are not shown in the TOC/Layers-panel. For instance, layers that can be used in joins or relationships (look-up tables). If you want to get those layers listed as well, do this:

# Iterate all registered layers (even if they aren't in the TOC)
def iterate_all_layers():
    for k, layer in QgsProject.instance().mapLayers().items():
        # TODO: Do something interesting with the layers
        print(layer.name())
            
iterate_all_layers()