What is the proper way to cite the usage of an API? For a grant I am writing, I need to describe how I mined data from social media sites. I collected data from sites such as Twitter using each site's API and a Python wrapper. In writing my methods, I assume that I should mention which APIs I used, or at least that I used an API. 

Do I need to provide a citation if I refer to using, say, the Python wrapper for Twitter's API. If so, how do I do that?
I don't think you'll find any documented correct way to do this. Personally, I would write a sentence saying that I did it, a sentence describing what an API is, and a link to the version-specific API documentation website (i.e., https://developers.google.com/youtube/v3/ for the API Version 3 instead of https://developers.google.com/youtube/ the general Youtube API help website).

If you're including code in the submission, consider adding the API code in an appendix.