upgrading default python version or install another python version in Linux

Question

I want to upgrade python's default version i.e /usr/bin/python in Linux.

I have multiple python versions installed as

/usr/bin/python2.7   
/usr/bin/python3.3

However, python command still returns python2.7

# python
Python 2.7 
Type "help", "copyright", "credits" or "license" for more information.
>>>

Now, I have installed a module, which got installed in the default version 2.7.

That's why I can't use python3.3 script.py, as it returns error for missing module.

How to update this default version to 3.3?

Is there a way to install the module in /usr/bin/python3.3 as well?

Added: Module is pexpect-2.3.

Solution

The accepted answer is good though, however I have found another hack trick to this problem and I think it's pretty simple.

At the location of /usr/bin/ there are many python related files available. You can see the file python is actually a link and it points to the python2(which is pointed to python2.7). So whenever you command python it calls the python2.7 not python3.5

The solution is to delete the original python link and make another link that points to python3.5 and make the newly link file name to python.

And you are done. :D

Comments

[Alex Chamberlain]

What version of Linux are you using? The only distribution that symlinks python to python3 is Arch AFAIK.

[Wooble]

How did you install the module? python3.3 setup.py install should do the right thing, if you installed from source.

[Wooble]

"Pexpect was written and tested with Python 2.5. It should work on earlier versions that have the pty module." would make me think there's no way it's going to run on Python 3.

[Wooble]

pexpect-u looks like a fork that does work on python 3; haven't tried it myself.

[Bakuriu]

Note that there is a reason why those distribution use python2 as reference for the python executable: some programs are still not python3 ready. While (e.g.) Ubuntu is putting a hardwork moving towards python3, it still has to update quite some of its components which means that doing what you describe will currently break a lot of your system. Hopefully in one or two years the major distributions will move to python3 only, but until then I don't think this is a good idea. Just specify python3 when launching your programs!