OK interesting, it actually appears to be written in RPython, not full Python:
https://github.com/jneen/tulip/blob/master/tulip/libedit.py
(RPython is the "static" subset of Python used to bootstrap PyPy)
Re:Tulip – An untyped functional language
by maxerickson on Friday March 27, 2015 @08:12PM
(#9279872)
They have moved towards treating RPython as a framework:
"Tulip is still in active development, and I could use a whole lot of help, both filling in the design gaps here and actually churning out the implementation"