Ubuntu – Trying to install spyder3, but getting spyder2

You can't install yet ack-grep 2.10 using apt-get because ack-grep 2.10 is not yet included in Ubuntu repositories. To see what versions are available in repositories, you can use the following command:

apt-cache showpkg ack-grep

But you can install by downloading it from here:

• http://packages.debian.org/sid/ack-grep

It's a deb file, so you can be interested also by:

• How do I install a .deb file via the command line?

Before Ubuntu adds python 3.5 to the official repositories you have two options to install it now :

• Check if someone has come with a PPA containing python 3.5 so that you can install/remove it using apt-get or other package manager

• Install from source

As fas as i can see there is no such PPA available till date so your only option is to install from source file.

You have said :

I don't want to do an old-school source install because that can make it harder to uninstall when the official packages come out.

Perhaps you have not heard of checkinstall yet, it creates a package out of the files that are going to be saved on different places in your computer at the last step of compiling a package from source (sudo make install). So you just need to replace sudo make install with sudo checkinstall and then you can remove the package you named using any package manager in the usual manner.

Check man checkinstall to get more idea.

Update:

A PPA is now available. Check this answer.