The Technology Enablement team (okay, mainly Marcos) has published an interesting number of PI Web API client libraries on GitHub, I have created this page so you can have quick access to those bits:
PI Web API client library for Python (still in development)
PI Web API client library for R (still in development)
If you have questions, please don't hesitate to ask!
DISCLAIMER: The GitHub repositories are examples of interesting things you may do with PI Developer Technologies. However, these client libraries are not official OSIsoft products. You are free to use the code, not use the code, or even modify the code as required by your own applications.