Why is "Python --version" command streaming the output to stderr instead of stdout?

Question

I have a virtual machine which runs centOs. When I am trying to redirect the stdout of "python --version" to a file, I am not seeing any data. But when I redirect the stderr to a file, I am able to see the python version.

[root@CM-DM-01 ~]# python --version > /tmp/out1
Python 2.6.6
[root@CM-DM-01 ~]# cat /tmp/out1
[root@CM-DM-01 ~]# python --version 2> /tmp/err1
[root@CM-DM-01 ~]# cat /tmp/err1
Python 2.6.6