How to get layer variables using QGIS Python APIs?

How can I access the layer variables defined by the user from QGIS Python APIs?

Answer

You may use the QgsExpressionContextUtils() class.

More in detail, you may set a new layer variable in this way:

layer = iface.activeLayer() # or similar way for loading a layer
QgsExpressionContextUtils.setLayerVariable(layer,'your_variable', 'John')

where layer is the layer object, your_variable is the name of the variable and John is the value of the variable.

For retrieving the value of the layer variable, you can use the following line:

QgsExpressionContextUtils.layerScope(layer).variable('your_variable')

In fact, if you run:

test = QgsExpressionContextUtils.layerScope(layer).variable('your_variable')
print test

you will get:

John

as desired.