[GIS] `NameError: name `qgis` is not defined` in QGIS Plugins

pyqgisqgis-3qgis-plugins

In the QGIS (2.99) Python Console, the name/variable qgis seems to be automatically defined.

However, in writing a plugin, there is an error whenever I refer to qgis. For example, in I have qgis.iface.mapCanvas() in my Plugin's `initGui(self)' function, I get an error

NameError: name `qgis` is not defined

How can fix this error?

By the way, I am trying to put the following code from this GIS.SE answer(https://gis.stackexchange.com/a/45105) into my plugin

tool = PointTool(qgis.iface.mapCanvas())
qgis.iface.mapCanvas().setMapTool(tool)

The code works fine inside QGIS main window (in Python Console), but generates the above error when moving it into the Plugin. I can't figure out how to let the PointTool respond inside a plugin. The code for PointTool class from the linked answer is:

class PointTool(QgsMapTool):   
    def __init__(self, canvas):
        QgsMapTool.__init__(self, canvas)
        self.canvas = canvas    

    def canvasPressEvent(self, event):
        pass

    ...

Best Answer

When you create a plugin, you receiv iface via the __init__ function :

def __init__(self, iface):
   self.iface = iface

After that in you code you can access to iface via self.iface.

Otherwise you can have access via qgis.utils.iface

Related Solutions

[GIS] Global name canvas is not defined

You are calling the wrong class. What you need to call is mapCanvas, and not canvas.

Change your code to this:

allLayers = iface.mapCanvas().layers()
for i in allLayers:
    print i.name()

This will print all of your current layers' names.

Also note that you need to indent the print line. I assume in your post this was just a copy/paste problem, but if not, go ahead and change it, or it will not work :-)

[GIS] NameError: name ‘QgsApplication’ is not defined in python standalone script

You're missing the import statement for the QgsApplication, add from qgis.core import QgsApplication. This may give you an ImportError if your qgis.core is not in your enviroment variables, the process to fix this vary depending on your operational system

Also, QgsApplication is a subclass from QApplication so you do not need to use both. Here's what you can do:

from PyQt4.QtGui import *
from PyQt4.QtCore import *
from qgis.core import QgsApplication, QgsMapCanvas, QgsVectorLayer, QgsMapLayerRegistry, QgsMapCanvasLayer
import sys, os

class Mapbox(QMainWindow):    
    def __init__(self, shapefile):
        QMainWindow.__init__(self)
        self.setWindowTitle("Map Box Viewer")
        canvas = QgsMapCanvas()
        canvas.useImageToRender(False)
        canvas.setCanvasColor(Qt.white)
        canvas.show()

        layer = QgsVectorLayer(shapefile, "layer1", "ogr")
        if not layer.isValid():
            raise IOError("Invalid shapefile")

        QgsMapLayerRegistry.instance().addMapLayer(layer)
        canvas.setExtent(layer.extent())
        canvas.setLayerSet([QgsMapCanvasLayer(layer)])        
        self.setCentralWidget(canvas)

app = QgsApplication(sys.argv, True)  # the second arg "True", says that you are using a interface
app.setPrefixPath("C:/OSGeo4W64/apps/qgis", True)  # Use forward slash in paths or os.path
app.initQgis()        
viewer = Mapbox(os.path.abspath("shapefile.shp"))  # QgsVectorLayer needs the absolute path to create a valid layer
viewer.show()

app.exec_()        
app.exit()

I have add some minor changes to the code.

Side note: QGis and PyQt are different things, PyQt is a python api of Qt. It is used to create interfaces, QGis makes use of PyQt to make its interfaces

Best Answer

Related Solutions

[GIS] Global name canvas is not defined

[GIS] NameError: name ‘QgsApplication’ is not defined in python standalone script

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