Getting current map scale in PyQGIS

Question

I'm trying to get the current map scale in PyQGIS, running outside QGIS, with:

project = QgsProject.instance()
root = project.layerTreeRoot()
canvas = QgsMapCanvas()
bridge = QgsLayerTreeMapCanvasBridge(root, canvas)
# project.read(projectpath)
canvas.center()
canvas.extent()
canvas.scale()

The center and the extent are just perfect! But the scale is quite different from the one reported at QGIS bottom bar.

Testing the same in QGIS gives the same result.

How do I get the current map scale in PyQGIS (3.x)?

I'm using a project coordinate system, using meters.

Answer 1

You need the canvas to be the same size for the scale to be the same.

Here is the small fragment of code

project = QgsProject.instance()
root = project.layerTreeRoot()
canvas = QgsMapCanvas()
bridge = QgsLayerTreeMapCanvasBridge(root, canvas)

canvas.setExtent(iface.mapCanvas().extent())
canvas.setCenter(iface.mapCanvas().center())
canvas.resize(iface.mapCanvas().size())

canvas.show()
canvas.scale()
#canvas.hide()