How do I get the scale of the map item in my Layout(composer) in Qgis3?

Question

I want to get the scale of my Layout that I created. For this I thought of using the QgsLayoutItemMap class. The problem is that the scale method in QgsLayoutItemMap always returns 0.0. I know I am doing something wrong but I don't know what. Here is the code I am using:

projectInstance = QgsProject.instance()
projectLayoutManager = projectInstance.layoutManager()
item = projectLayoutManager.layoutByName("asd")
tail = QgsLayoutItemMap(item)
tail.scale()

Answer 1

I solved the mystery about the scale. First I have to search for the layout I want to use:

projectInstance = QgsProject.instance()
projectLayoutManager = projectInstance.layoutManager()
projectLayoutManager.layouts()

With this we get all layouts that we have. Then we chose which one we want to use.

layout = projectLayoutManager.layouts()[0]   #chose layout

The method referenceMap in QgsLayout is what we need now. Let's say our layout is a QgsPrintLayout. Because QgsPrintLayout inherits all methods from QgsLayout, we can use the referenceMap method and that will help us use the scale method in QgsLayoutItemMap. And then we can use our scale method to get our scale. Here is the rest of the code:

referencemap = layout.referenceMap()
referencemap.scale()

Answer 2

Your solution is using Python. I'm gonna give how to get the scale using a QGIS Expresion only:

First, set a ITEM ID on your map item, in the tab properties:

Then, in your label, you the expression:

 [% map_get(item_variables( 'map1' ), 'map_scale') %]

This is will output the scale of the map called 'map1'.