  We describe pynucastro 2.0, an open source library for interactively creating
and exploring astrophysical nuclear reaction networks. We demonstrate new
methods for approximating rates and using detailed balance to create reverse
rates, show how to build networks and determine whether they are appropriate
for a particular science application, and discuss the changes made to the
library over the past few years. Finally, we demonstrate the validity of the
networks produced and share how we use pynucastro networks in simulation codes.
