Well a problem shared is a problem halved, right?
This isn't the total solution but more a case of bringing you up to speed with where I'm at with this.
First, I run Linux Mint at home. This is derived from Linux Ubuntu which in turn is derived from Linux Debian. (One of the great things about linux is the way it evolves both within a distribution and by forking new distributions)
So.. in linux we have what is called 'The Package Manager' sometimes called 'Synaptic'. From there its really easy to find Python 3 x and install it on a pc or laptop. Most distributions come packaged with 2.7 anyway but upgrading to 3x is really as simple as ticking a box and then 'install'.
Synaptic is essentially a list of softwares available from various repositories that it regularly accesses and updates. Which brings us to the operating system on the Yun which you have no doubt deduced is called Linino - a Debian derivative. However it doesn't have Python 3.3 in its repositories. That doesn't mean we're dead in the water because most linux distributions have the facility to add a repo (Called a PPA).
So the way I see things now is that we need to figure out if we can add a compatible repo to lininio (Fedora, Suse etc use different repo's to Debian, Ubuntu etc - mostly)
This is my next task after figuring out how to access the terminal (Similar to the old DOS window you may remember) because if we can, we might be able to add the repo we need.
Its a long shot but I'm hopeful of a result. I have a busy week ahead but I'll see if I can suss it out. If I can, I will post step by step instructions on here.
I should add that if I do crack it and post a how to, I am not liable for your Yun!!!
Anyway, leave it with me for a few days and lets see what gives. In the meantime heres a page that shows how to install it 'longhand' on ubuntu. Its much simpler than this with synaptic but like most things its probably worth learning the nuts and bolts method because it may be the way we need to go about things. Remember, this page is not about installing on a tun, its about installing on a pc. We have to figure out how to do exactly this on the Yun. The page: http://www.unixmen.com/howto-install-python-3-x-in-ubuntu-debian-fedora-centos/
I hope you didn't mind the lengthy answer but I figured as a nebie to Linux, some background info and explanation might be helpful.