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In the case of the sidebar snapins, the file ~/lib/python3/cmk/gui/plugins/config/base.py doesn't help us because the variable "sidebar" that is set there seems to have a new data structure. You can find out this structure by explicitly configuring your sidebar in the GUI and then checking out the file ~/var/check_mk/web/<your_username>/sidebar.mk. The structure you find there can be used in ~/local/share/check_mk/web/plugins/config/my_base.py:
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