21. Cheat sheet for PyQGIS
Hint
The code snippets on this page need the following imports if you’re outside the pyqgis console:
1from qgis.PyQt.QtCore import (
2 QRectF,
3)
4
5from qgis.core import (
6 Qgis,
7 QgsProject,
8 QgsLayerTreeModel,
9)
10
11from qgis.gui import (
12 QgsLayerTreeView,
13)
21.1. User Interface
Change Look & Feel
1from qgis.PyQt.QtWidgets import QApplication
2
3app = QApplication.instance()
4app.setStyleSheet(".QWidget {color: blue; background-color: yellow;}")
5# You can even read the stylesheet from a file
6with open("testdata/file.qss") as qss_file_content:
7 app.setStyleSheet(qss_file_content.read())
Change icon and title
1from qgis.PyQt.QtGui import QIcon
2
3icon = QIcon("/path/to/logo/file.png")
4iface.mainWindow().setWindowIcon(icon)
5iface.mainWindow().setWindowTitle("My QGIS")
21.2. Settings
Get QgsSettings list
1from qgis.core import QgsSettings
2
3qs = QgsSettings()
4
5for k in sorted(qs.allKeys()):
6 print (k)
21.3. Toolbars
Remove toolbar
1toolbar = iface.helpToolBar()
2parent = toolbar.parentWidget()
3parent.removeToolBar(toolbar)
4
5# and add again
6parent.addToolBar(toolbar)
Remove actions toolbar
actions = iface.attributesToolBar().actions()
iface.attributesToolBar().clear()
iface.attributesToolBar().addAction(actions[4])
iface.attributesToolBar().addAction(actions[3])
21.5. Canvas
Access canvas
canvas = iface.mapCanvas()
Change canvas color
from qgis.PyQt.QtCore import Qt
iface.mapCanvas().setCanvasColor(Qt.black)
iface.mapCanvas().refresh()
Map Update interval
from qgis.core import QgsSettings
# Set milliseconds (150 milliseconds)
QgsSettings().setValue("/qgis/map_update_interval", 150)
21.6. Layers
Add vector layer
layer = iface.addVectorLayer("testdata/airports.shp", "layer name you like", "ogr")
if not layer or not layer.isValid():
print("Layer failed to load!")
Get active layer
layer = iface.activeLayer()
List all layers
from qgis.core import QgsProject
QgsProject.instance().mapLayers().values()
Obtain layers name
1from qgis.core import QgsVectorLayer
2layer = QgsVectorLayer("Point?crs=EPSG:4326", "layer name you like", "memory")
3QgsProject.instance().addMapLayer(layer)
4
5layers_names = []
6for layer in QgsProject.instance().mapLayers().values():
7 layers_names.append(layer.name())
8
9print("layers TOC = {}".format(layers_names))
layers TOC = ['layer name you like']
Otherwise
layers_names = [layer.name() for layer in QgsProject.instance().mapLayers().values()]
print("layers TOC = {}".format(layers_names))
layers TOC = ['layer name you like']
Find layer by name
from qgis.core import QgsProject
layer = QgsProject.instance().mapLayersByName("layer name you like")[0]
print(layer.name())
layer name you like
Set active layer
from qgis.core import QgsProject
layer = QgsProject.instance().mapLayersByName("layer name you like")[0]
iface.setActiveLayer(layer)
Refresh layer at interval
1from qgis.core import QgsProject
2
3layer = QgsProject.instance().mapLayersByName("layer name you like")[0]
4# Set seconds (5 seconds)
5layer.setAutoRefreshInterval(5000)
6# Enable data reloading
7layer.setAutoRefreshMode(Qgis.AutoRefreshMode.ReloadData)
Show methods
dir(layer)
Adding new feature with feature form
1from qgis.core import QgsFeature, QgsGeometry
2
3feat = QgsFeature()
4geom = QgsGeometry()
5feat.setGeometry(geom)
6feat.setFields(layer.fields())
7
8iface.openFeatureForm(layer, feat, False)
Adding new feature without feature form
1from qgis.core import QgsGeometry, QgsPointXY, QgsFeature
2
3pr = layer.dataProvider()
4feat = QgsFeature()
5feat.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(10,10)))
6pr.addFeatures([feat])
Get features
for f in layer.getFeatures():
print (f)
<qgis._core.QgsFeature object at 0x7f45cc64b678>
Get selected features
for f in layer.selectedFeatures():
print (f)
Get selected features Ids
selected_ids = layer.selectedFeatureIds()
print(selected_ids)
Create a memory layer from selected features Ids
from qgis.core import QgsFeatureRequest
memory_layer = layer.materialize(QgsFeatureRequest().setFilterFids(layer.selectedFeatureIds()))
QgsProject.instance().addMapLayer(memory_layer)
Get geometry
# Point layer
for f in layer.getFeatures():
geom = f.geometry()
print ('%f, %f' % (geom.asPoint().y(), geom.asPoint().x()))
10.000000, 10.000000
Move geometry
1from qgis.core import QgsFeature, QgsGeometry
2poly = QgsFeature()
3geom = QgsGeometry.fromWkt("POINT(7 45)")
4geom.translate(1, 1)
5poly.setGeometry(geom)
6print(poly.geometry())
<QgsGeometry: Point (8 46)>
Set the CRS
from qgis.core import QgsProject, QgsCoordinateReferenceSystem
for layer in QgsProject.instance().mapLayers().values():
layer.setCrs(QgsCoordinateReferenceSystem('EPSG:4326'))
See the CRS
1from qgis.core import QgsProject
2
3for layer in QgsProject.instance().mapLayers().values():
4 crs = layer.crs().authid()
5 layer.setName('{} ({})'.format(layer.name(), crs))
Hide a field column
1from qgis.core import QgsEditorWidgetSetup
2
3def fieldVisibility (layer,fname):
4 setup = QgsEditorWidgetSetup('Hidden', {})
5 for i, column in enumerate(layer.fields()):
6 if column.name()==fname:
7 layer.setEditorWidgetSetup(idx, setup)
8 break
9 else:
10 continue
Layer from WKT
1from qgis.core import QgsVectorLayer, QgsFeature, QgsGeometry, QgsProject
2
3layer = QgsVectorLayer('Polygon?crs=epsg:4326', 'Mississippi', 'memory')
4pr = layer.dataProvider()
5poly = QgsFeature()
6geom = QgsGeometry.fromWkt("POLYGON ((-88.82 34.99,-88.09 34.89,-88.39 30.34,-89.57 30.18,-89.73 31,-91.63 30.99,-90.87 32.37,-91.23 33.44,-90.93 34.23,-90.30 34.99,-88.82 34.99))")
7poly.setGeometry(geom)
8pr.addFeatures([poly])
9layer.updateExtents()
10QgsProject.instance().addMapLayers([layer])
Load all vector layers from GeoPackage
1from qgis.core import QgsDataProvider
2
3fileName = "testdata/sublayers.gpkg"
4layer = QgsVectorLayer(fileName, "test", "ogr")
5subLayers = layer.dataProvider().subLayers()
6
7for subLayer in subLayers:
8 name = subLayer.split(QgsDataProvider.SUBLAYER_SEPARATOR)[1]
9 uri = "%s|layername=%s" % (fileName, name,)
10 # Create layer
11 sub_vlayer = QgsVectorLayer(uri, name, 'ogr')
12 # Add layer to map
13 QgsProject.instance().addMapLayer(sub_vlayer)
Load tile layer (XYZ-Layer)
1from qgis.core import QgsRasterLayer, QgsProject
2
3def loadXYZ(url, name):
4 rasterLyr = QgsRasterLayer("type=xyz&url=" + url, name, "wms")
5 QgsProject.instance().addMapLayer(rasterLyr)
6
7urlWithParams = 'https://tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.png&zmax=19&zmin=0&crs=EPSG3857'
8loadXYZ(urlWithParams, 'OpenStreetMap')
Remove all layers
QgsProject.instance().removeAllMapLayers()
Remove all
QgsProject.instance().clear()
21.7. Table of contents
Access checked layers
iface.mapCanvas().layers()
Remove contextual menu
1ltv = iface.layerTreeView()
2mp = ltv.menuProvider()
3ltv.setMenuProvider(None)
4# Restore
5ltv.setMenuProvider(mp)
21.8. Advanced TOC
Root node
1from qgis.core import QgsVectorLayer, QgsProject, QgsLayerTreeLayer
2
3root = QgsProject.instance().layerTreeRoot()
4node_group = root.addGroup("My Group")
5
6layer = QgsVectorLayer("Point?crs=EPSG:4326", "layer name you like", "memory")
7QgsProject.instance().addMapLayer(layer, False)
8
9node_group.addLayer(layer)
10
11print(root)
12print(root.children())
Access the first child node
1from qgis.core import QgsLayerTreeGroup, QgsLayerTreeLayer, QgsLayerTree
2
3child0 = root.children()[0]
4print (child0.name())
5print (type(child0))
6print (isinstance(child0, QgsLayerTreeLayer))
7print (isinstance(child0.parent(), QgsLayerTree))
My Group
<class 'qgis._core.QgsLayerTreeGroup'>
False
True
Find groups and nodes
1from qgis.core import QgsLayerTreeGroup, QgsLayerTreeLayer
2
3def get_group_layers(group):
4 print('- group: ' + group.name())
5 for child in group.children():
6 if isinstance(child, QgsLayerTreeGroup):
7 # Recursive call to get nested groups
8 get_group_layers(child)
9 else:
10 print(' - layer: ' + child.name())
11
12
13root = QgsProject.instance().layerTreeRoot()
14for child in root.children():
15 if isinstance(child, QgsLayerTreeGroup):
16 get_group_layers(child)
17 elif isinstance(child, QgsLayerTreeLayer):
18 print ('- layer: ' + child.name())
- group: My Group
- layer: layer name you like
Find group by name
print (root.findGroup("My Group"))
<QgsLayerTreeGroup: My Group>
Find layer by id
print(root.findLayer(layer.id()))
<QgsLayerTreeLayer: layer name you like>
Add layer
1from qgis.core import QgsVectorLayer, QgsProject
2
3layer1 = QgsVectorLayer("Point?crs=EPSG:4326", "layer name you like 2", "memory")
4QgsProject.instance().addMapLayer(layer1, False)
5node_layer1 = root.addLayer(layer1)
6# Remove it
7QgsProject.instance().removeMapLayer(layer1)
Add group
1from qgis.core import QgsLayerTreeGroup
2
3node_group2 = QgsLayerTreeGroup("Group 2")
4root.addChildNode(node_group2)
5QgsProject.instance().mapLayersByName("layer name you like")[0]
Move loaded layer
1layer = QgsProject.instance().mapLayersByName("layer name you like")[0]
2root = QgsProject.instance().layerTreeRoot()
3
4myLayer = root.findLayer(layer.id())
5myClone = myLayer.clone()
6parent = myLayer.parent()
7
8myGroup = root.findGroup("My Group")
9# Insert in first position
10myGroup.insertChildNode(0, myClone)
11
12parent.removeChildNode(myLayer)
Move loaded layer to a specific group
1QgsProject.instance().addMapLayer(layer, False)
2
3root = QgsProject.instance().layerTreeRoot()
4myGroup = root.findGroup("My Group")
5myOriginalLayer = root.findLayer(layer.id())
6myLayer = myOriginalLayer.clone()
7myGroup.insertChildNode(0, myLayer)
8parent.removeChildNode(myOriginalLayer)
Toggling active layer visibility
root = QgsProject.instance().layerTreeRoot()
node = root.findLayer(layer.id())
new_state = Qt.Checked if node.isVisible() == Qt.Unchecked else Qt.Unchecked
node.setItemVisibilityChecked(new_state)
Is group selected
1def isMyGroupSelected( groupName ):
2 myGroup = QgsProject.instance().layerTreeRoot().findGroup( groupName )
3 return myGroup in iface.layerTreeView().selectedNodes()
4
5print(isMyGroupSelected( 'my group name' ))
False
Expand node
print(myGroup.isExpanded())
myGroup.setExpanded(False)
Hidden node trick
1from qgis.core import QgsProject
2
3model = iface.layerTreeView().layerTreeModel()
4ltv = iface.layerTreeView()
5root = QgsProject.instance().layerTreeRoot()
6
7layer = QgsProject.instance().mapLayersByName('layer name you like')[0]
8node = root.findLayer(layer.id())
9
10index = model.node2index( node )
11ltv.setRowHidden( index.row(), index.parent(), True )
12node.setCustomProperty( 'nodeHidden', 'true')
13ltv.setCurrentIndex(model.node2index(root))
Node signals
1def onWillAddChildren(node, indexFrom, indexTo):
2 print ("WILL ADD", node, indexFrom, indexTo)
3
4def onAddedChildren(node, indexFrom, indexTo):
5 print ("ADDED", node, indexFrom, indexTo)
6
7root.willAddChildren.connect(onWillAddChildren)
8root.addedChildren.connect(onAddedChildren)
Remove layer
root.removeLayer(layer)
Remove group
root.removeChildNode(node_group2)
Create new table of contents (TOC)
1root = QgsProject.instance().layerTreeRoot()
2model = QgsLayerTreeModel(root)
3view = QgsLayerTreeView()
4view.setModel(model)
5view.show()
Move node
cloned_group1 = node_group.clone()
root.insertChildNode(0, cloned_group1)
root.removeChildNode(node_group)
Rename node
cloned_group1.setName("Group X")
node_layer1.setName("Layer X")
21.9. Processing algorithms
Get algorithms list
1from qgis.core import QgsApplication
2
3for alg in QgsApplication.processingRegistry().algorithms():
4 if 'buffer' == alg.name():
5 print("{}:{} --> {}".format(alg.provider().name(), alg.name(), alg.displayName()))
QGIS (native c++):buffer --> Buffer
Get algorithms help
Random selection
from qgis import processing
processing.algorithmHelp("native:buffer")
...
Run the algorithm
For this example, the result is stored in a temporary memory layer which is added to the project.
from qgis import processing
result = processing.run("native:buffer", {'INPUT': layer, 'OUTPUT': 'memory:'})
QgsProject.instance().addMapLayer(result['OUTPUT'])
Processing(0): Results: {'OUTPUT': 'output_d27a2008_970c_4687_b025_f057abbd7319'}
How many algorithms are there?
len(QgsApplication.processingRegistry().algorithms())
How many providers are there?
from qgis.core import QgsApplication
len(QgsApplication.processingRegistry().providers())
How many expressions are there?
from qgis.core import QgsExpression
len(QgsExpression.Functions())
21.10. Decorators
CopyRight
1from qgis.PyQt.Qt import QTextDocument
2from qgis.PyQt.QtGui import QFont
3
4mQFont = "Sans Serif"
5mQFontsize = 9
6mLabelQString = "© QGIS 2019"
7mMarginHorizontal = 0
8mMarginVertical = 0
9mLabelQColor = "#FF0000"
10
11INCHES_TO_MM = 0.0393700787402 # 1 millimeter = 0.0393700787402 inches
12case = 2
13
14def add_copyright(p, text, xOffset, yOffset):
15 p.translate( xOffset , yOffset )
16 text.drawContents(p)
17 p.setWorldTransform( p.worldTransform() )
18
19def _on_render_complete(p):
20 deviceHeight = p.device().height() # Get paint device height on which this painter is currently painting
21 deviceWidth = p.device().width() # Get paint device width on which this painter is currently painting
22 # Create new container for structured rich text
23 text = QTextDocument()
24 font = QFont()
25 font.setFamily(mQFont)
26 font.setPointSize(int(mQFontsize))
27 text.setDefaultFont(font)
28 style = "<style type=\"text/css\"> p {color: " + mLabelQColor + "}</style>"
29 text.setHtml( style + "<p>" + mLabelQString + "</p>" )
30 # Text Size
31 size = text.size()
32
33 # RenderMillimeters
34 pixelsInchX = p.device().logicalDpiX()
35 pixelsInchY = p.device().logicalDpiY()
36 xOffset = pixelsInchX * INCHES_TO_MM * int(mMarginHorizontal)
37 yOffset = pixelsInchY * INCHES_TO_MM * int(mMarginVertical)
38
39 # Calculate positions
40 if case == 0:
41 # Top Left
42 add_copyright(p, text, xOffset, yOffset)
43
44 elif case == 1:
45 # Bottom Left
46 yOffset = deviceHeight - yOffset - size.height()
47 add_copyright(p, text, xOffset, yOffset)
48
49 elif case == 2:
50 # Top Right
51 xOffset = deviceWidth - xOffset - size.width()
52 add_copyright(p, text, xOffset, yOffset)
53
54 elif case == 3:
55 # Bottom Right
56 yOffset = deviceHeight - yOffset - size.height()
57 xOffset = deviceWidth - xOffset - size.width()
58 add_copyright(p, text, xOffset, yOffset)
59
60 elif case == 4:
61 # Top Center
62 xOffset = deviceWidth / 2
63 add_copyright(p, text, xOffset, yOffset)
64
65 else:
66 # Bottom Center
67 yOffset = deviceHeight - yOffset - size.height()
68 xOffset = deviceWidth / 2
69 add_copyright(p, text, xOffset, yOffset)
70
71# Emitted when the canvas has rendered
72iface.mapCanvas().renderComplete.connect(_on_render_complete)
73# Repaint the canvas map
74iface.mapCanvas().refresh()
21.11. Composer
Get print layout by name
1composerTitle = 'MyComposer' # Name of the composer
2
3project = QgsProject.instance()
4projectLayoutManager = project.layoutManager()
5layout = projectLayoutManager.layoutByName(composerTitle)