QGIS Python Snippets

qgis_scripting_snippets.py

# Layer from Memory
layer =  QgsVectorLayer('Point?crs=epsg:4326', 'MyPoint' ,'memory')
pr = layer.dataProvider()
pt = QgsFeature()
point1 = QgsPoint(-35.92,-7.24)
pt.setGeometry(QgsGeometry.fromPoint(point1))
pr.addFeatures([pt])
layer.updateExtents()
QgsMapLayerRegistry.instance().addMapLayers([layer])


from PyQt4.QtCore import *
from PyQt4.QtGui import *
from qgis.core import *
from qgis.gui import *

# Adding a polygon
def run_script(iface):
    layer = QgsVectorLayer('Polygon?crs=epsg:4326', 'AI', "memory")
    pr = layer.dataProvider()
    poly = QgsFeature()
    geom = QgsGeometry.fromWkt("POLYGON((-35.94197 -7.25673, -35.94118 -7.21712, -35.88810 -7.21830, -35.88849 -7.25713, -35.94197 -7.25673))")
    poly.setGeometry(geom)
    pr.addFeatures([poly])
    layer.updateExtents()
    QgsMapLayerRegistry.instance().addMapLayers([layer])
    
run_script(iface)


# Loading a vector layer from file sample
data = "/home/marcello/qgis_data/NYC_MUSEUMS_GEO.shp"
layer = QgsVectorLayer(data,"New York City Museums", "ogr")

if not layer.isValid():
    print "Layer %s did not load" % layer.name()
    
QgsMapLayerRegistry.instance().addMapLayers([layer])


# Loading a vector layer from Database (PostgreSQL)
uri = QgsDataSourceURI()
uri.setConnection("localhost", "5432", "sample", "postgres", "postgres")
uri.setDataSource ("public", "municipios", "geom")

layer = QgsVectorLayer(uri.uri(False), "municipios", "postgres")

if not layer.isValid():
    print "Layer %s did not load" % layer.name()

QgsMapLayerRegistry.instance().addMapLayers([layer])


# Examining vector layer attributes
data = "/home/marcello/qgis_data/NYC_MUSEUMS_GEO.shp"

layer = QgsVectorLayer(data,"New York City Museums", "ogr")

iter = layer.getFeatures()

for feature in iter:
    geom = feature.geometry().asPoint()
    x, y  = (tuple(geom))
    print("x: {}, y: {}".format(x, y))
    print(feature.attributes())
    print("-=" * 20)