I am trying to select features of a layer based on an expression that uses the variable jenks_var_sep_minclass. When running it I don't get an error message, but there are also no features selected even though some of their attribute values are in the range that is supposed to be selected.
When I run the code using a number instead of the variable for the expression, everything works well.
# create list of area attributes
area_list = [feature.attributes()[1] for feature in layer.getFeatures()]
# calculate Jenks Natural Breaks and assign second value as variable
jenks_breaks = jenkspy.jenks_breaks(area_list, nb_class=10)
jenks_var_sep_minclass = float(jenks_breaks[1])
print(jenks_var_sep_minclass)
# Select
layer = iface.activeLayer()
layer.selectByExpression('"Area" > jenks_var_sep_minclass', QgsVectorLayer.SetSelection)
'"Area" > {}'.format(jenks_var_sep_minclass). In your version of the expression you're passing the variable as a simple string in the expression, so it never gets evaluated.