For your information, I just sent emails to Julien, Cheryl and Sanyam to notify them that I will their mentor during one month.
I asked them to ask me to double check before merging a pull request (Julien) or closing a bug (Cheryl and Sanyam).
Since I'm trying for formalize the whole process to become a core dev, I kept a copy of my emails to serve as template for future mentors:
By the way, I'm now working on the "Process to become a core developer" document (maybe becoming a PEP later?) at: https://github.com/vstinner/misc/blob/master/cpython/pep-core_dev_process.rs... (I almost didn't change since I sent it to python-committers)