Certbot Error while running on CentOS 7. Error: pkg_resources.DistributionNotFound: mock

I have installed certbot on my CentOS 7 VPS server using the command # *yum install certbot* after installation got the message Package certbot-1.11.0-2.el7.noarch already installed and latest version

And when trying to run # *certbot* command on my server getting the following error.

Traceback (most recent call last):
  File "/usr/bin/certbot", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 3007, in <module>
    working_set.require(__requires__)
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 728, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 626, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: mock

mock package is already installed on my server # rpm -qa |grep mock easymock2-2.5.2-12.el7.noarch python2-mock-1.0.1-10.el7.noarch

Any solution to run certbot ?