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It basically uses GDB to call eval inside a running Python VM. Pretty simple, but quite useful from time to time.

But how does it get into that running Python VM?

GDB uses a system call(s) to attach to the running process[1], and python exposes an API that lets you evaluate code in the current VM context[2]. Specifically, https://github.com/lmacken/pyrasite/blob/develop/pyrasite/in...

[1] http://aosabook.org/en/gdb.html [2] https://docs.python.org/2/c-api/veryhigh.html

Excellent answer to my question. Thanks!

It's basically this: attach with GDB, get GIL, run commands (your session), release GIL. This is pretty dangerous as the GIL release is not guaranteed.

This is why I wrote https://pypi.python.org/pypi/manhole - I couldn't afford hosing up (deadlocking) my processes, and it happen pretty often with pyrasite in my usecases. Have in mind that manhole is not that flexible as it uses different technique.

Just read this file: https://github.com/lmacken/pyrasite/blob/develop/pyrasite/in... it's rather straightforward.