Interactive shell to a running Python process

Yes, pyrasite does just that with a python wrapper around the gdb commands.

https://fedorahosted.org/pyrasite/

It was discussed here:

http://news.ycombinator.com/item?id=3014484

See the albertzeyer comment.

And Twisted has Manhole, but for some reason we were never allowed to enable it on production deployments...

We've been using rfoo to do this. It doesn't seem to impact performance when you're not using it. When you are using it, it's unsafe if you do unsafe things. We primarily use it for debugging by passively inspecting the messed-up portion of the server's state.

> is it unsafe, etc.?

As the readme notes, it's completely unsafe if you perform any mutation operation.

As to the performance hit, I'd expect almost none when not in use for long-running processes: it spawns a thread, and that thread will then wait on a socket accept, no connection, no resources spent. You'll still be paying in memory for the server thread, but that's it (the server thread only creates two objects, an rlcompleter.Completer instance and a function).

For ObjC:

https://github.com/albertz/Pyjector (and then access the ObjC runtime via the Python ObjC bridge)

https://github.com/albertz/FScriptAnywhereSIMBL

Objective-C also has Cycript at http://cycript.org/, which has a hybrid syntax of JavaScript and Objective-C and supports injecting into any running process.b

It's dead easy in Node using the REPL module (http://nodejs.org/docs/v0.6.5/api/repl.html). I've used this to debug weird async issues.

Ruby's had the much more featureful Pry for some time now: http://github.com/pry/pry.

(And there have been various projects to provide some sub-capabilities for years.)

Id like to see it in bash, all i know now is to use the +x option but you need to do it before its run

With Perl you would use Enbugger & gdb using these instructions: https://metacpan.org/module/Enbugger#From-gdb