I'm trying to install library using (sudo apt-get install python-tk ) this error appears
E: The list of sources could not be read.
E: Malformed line 1 in source list /etc/apt/sources.list.d/gazebo-stable.list (type)
and i don't know what should be written in this file currently this is written in it
deb
http://packages.osrfoundation.org/gazebo/ubuntu-stable focal
main