reason

Upgrading to python3.6 will result in confusion of references to Python libraries

resolvent

Select Delete Python apt first

apt-get remove --purge python-apt 

Install Python apt

apt-get install -f -y python-apt

Copy the apt PKG *. So name of python3.5 and rename it apt PKG *. So of python3.6

cd /usr/lib/python3/dist-packages/
cp apt_pkg.cpython-35m-x86_64-linux-gnu.so apt_pkg.cpython-36m-x86_64-linux-gnu.so