I have the same problem.
Yum has been written in Python lang.
So when you upgrade your default Python to new version it will make problem for yum.
If you get python --version it will tell you 3.3.
For solving this problem , change python command to python2.7.
First check it:
user@host:~$ ls -l /usr/bin/python
lrwxrwxrwx 1 root root 9 Sep 28 2013 /usr/bin/python -> python3.3
Try it:
mv /usr/bin/python /usr/bin/python-origin
ln -s python2.7 /usr/bin/python
Then check it:
user@host:~$ ls -l /usr/bin/python
lrwxrwxrwx 1 root root 9 Sep 28 2013 /usr/bin/python -> python2.7
If you wish to install python3 in CentOS you should install that via source code.
download main source code via python.org website.
extract archive file.
./configure
make
make install
