It is little difficult for upgrading Python in cpanel servers. Because if you  upgrade python directly , the yum package manager will not  work. So  you need to reinstall all old rpms again.

When you required to upgrade python on Cpanel server?
The latest  Mailman have some bugs. It need Python version of 2.4.6 at least. But in your centos4/RHEL4 servers the python version is  2.4.3. So for fixing the mail man issue you need to upgrade the python without  breaking  Yum and other python modules.

Please proceed with the following for upgrading Python

1) Download and install python 2.4.6

# cd /usr/local/src/
# wget  http://www.python.org/ftp/python/2.4.6/Python-2.4.6.tgz
# tar -xvzf Python-2.4.6.tgz
# cd Python-2.4.6/
# ./configure –prefix=/usr/local/python.2.4.6/
# make
# make install

2) Configure cpanel for latest Python as follows

# grep python /var/cpanel/cpanel.config
#python=/usr/local/bin/python2.4
python=/usr/local/python.2.4.6/bin/python2.4
3) Now reinstall Mailman
# /scripts/reinstallmailman

This will fix your issue