installing modules through paver in python

When using paver for python build, how can i write a conditional for checking if my user has the required installed modules? If not then to be able to install it through the script. This should be written in pavement.py.

For an example, I am working with requests. when my user runs the build through paver, I want to be able to check to see if requests needs to installed. like using pip but in a paver script.

I have tried to find examples on paver documentation. I was not able to find any good examples or information.