Update Python 3.5 to 3.6 via terminal

I had the same problem, I did the following instruction to resolve it:

After installing Python3.6:

To make python3 use the new installed Python 3.6 instead of the default 3.5 release, run following 2 commands:

sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.5 1

sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 2

Finally, switch between the two Python versions for python3 via the following command:

sudo update-alternatives --config python3

Then select the /usr/bin/python3.6 -- automode in choices menu, for me that was 0 row.

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[Result]:

$ python3 -V
Python 3.6.9

Or:

$ python3 --version
Python 3.6.9

How did you upgrade? I suspect you may have a python3.6 binary somewhere.

Generally speaking, you never want to replace /usr/bin/python or /usr/bin/python3 with your own fruity versions. Important parts of Ubuntu require their stable Python environments, and largely speaking, that is incompatible with you mucking around.

That all said, having a /usr/bin/python3.6 (or /usr/local/bin/python3.6, or whatever in your path) would be fine. If you don't want to type all that in each time, you might want to look at virtualenv and the various wrapper automation options for it. This has the additional bonus of not threatening your system's site_packages with your development work.

Installing and upgrading to Python3.6 requires the command

sudo apt-get upgrade python3.6