Python's support for multithreaded programs has improved considerably over
the last few years with the advent of the <a
href="https://lwn.net/Articles/1078367/">"free-threaded" version of the language</a>. But
testing multithreaded programs is notoriously difficult, because the
underlying host system determines the thread-execution ordering, which adds
an element of non-determinism. At PyCon US, Larry Hastings gave a talk (<a
href="https://www.youtube.com/watch?v=S3LUpx0hzkw&t=96s">YouTube video</a>)
about his <a href="https://pypi.org/project/blanket/">blanket</a> project,
which is meant to provide mechanisms for deterministic testing of
multithreaded Python code.