Depending on what state cpython is in when you inject, pyrasite may deadlock or segfault the interpreter. All it does is try to get the GIL and then inject the code.

Pyringe first gets to a safe place before injecting by (essentially) faking the delivery of a signal, then waiting for python-level signal handler dispatch to trigger. By doing so, it ensures the interpreter first gets itself into a state in which it can execute arbitrary python code before performing the injection.

Pyrasite has a bunch of features pyringe doesn't, though.