Labels not displaying for layers inside group using ArcPy

Question

I'm using a python script to create an empty group layer in the current map document, add some layers to this group and update their symbology from an existing .lyr file.

I also want to to turn on these layers' labels using layer.showLabels = True and it works fine for normal layers, but for some reason it doesn't work on layers inside a group layer. However, when I manually drag these layers outside of the group, the labels are suddenly displayed, and they are still displayed when I drag the layers back into the group.

Why does it happen and how can I programmatically display the labels even for layers inside a group?

Here is the relevant part (of a simplified version) of my ode:

mxd = arcpy.mapping.MapDocument("Current")
df = arcpy.mapping.ListDataFrames(mxd)[0]
groupLyr = arcpy.mapping.Layer(r'C:\Path\to\Group.lyr') # this is an empty group lyr file

arcpy.mapping.AddLayer(df,groupLyr)
currentGroup = arcpy.mapping.ListLayers(mxd,"Group")[0]

source_fc = arcpy.mapping.Layer(r'C:\Path\to\my.gdb\feature_class')
arcpy.mapping.AddLayerToGroup(df, currentGroup, source_fc, "BOTTOM")

lyr = arcpy.mapping.ListLayers(mxd,"[my layer's name]")[0]
lyr.showLabels = True # this line doesn't raise an error, but it does not turns the labels on

Answer 1

Add the line arcpy.RefreshActiveView() to the end of the script. (Or choose "Refresh" from the "View" menu in ArcMap.)

ArcMap does not automatically redraw the map after each and every script command. But it does redraw the map if you move a layer using the GUI Table of Contents, as you've described moving the layers out-of/into the group.

The arcpy.RefreshActiveView() call tells ArcMap that the map should be redrawn (usually because something has changed, such as labels).

See the documentation at RefreshActiveView which says:

Summary

Refreshes the active view and table of contents of the current map document.

Discussion

RefreshActiveView is only needed if you want to see the active view of the current map document updated.

If ArcMap did automatically refresh the view each time an arcpy.mapping function was executed, it could end up refreshing the view multiple times during the script (eg, after you added the group layer, after you added the layer to the group and after you turned labels on). Each refresh takes time, and in some maps this can be a LOT of time. Therefore, it is up to you to decide when the map needs refreshing.

The code I tested with (in a script tool in ArcMap 10.7.1) is below:

import arcpy

mxd = arcpy.mapping.MapDocument("Current")
df = arcpy.mapping.ListDataFrames(mxd)[0]
groupLyr = arcpy.mapping.Layer(r'C:\Group.lyr')

arcpy.mapping.AddLayer(df,groupLyr)
currentGroup = arcpy.mapping.ListLayers(mxd,"Group")[0]

source_fc = arcpy.mapping.Layer(r'C:\fGDB.gdb\FeatureClass')
arcpy.mapping.AddLayerToGroup(df, currentGroup, source_fc, "BOTTOM")

lyr = arcpy.mapping.ListLayers(mxd,"FeatureClass")[0]
lyr.showLabels = True

arcpy.RefreshActiveView()