[versteegen]

What's being asked is, after defining the missing function, whether it's possible to clear the exception and continue the execution without having to restart from the beginning. This is very useful when you hit an exception after 10 minutes of execution. (This is a real usecase which would have saved me untold hours.)

I hope it's possible somehow, but if you just load pdb (e.g. with %pdb in ipython), pdb is entered in post-mortem mode, from which it's impossible to modify code/data and resume execution. Setting a breakpoint (or pdb.set_trace()) would requiring knowing about the bug ahead of time. Does it only work when interrupting with a remote debugger rather than on exception?

However, it wouldn't be possible if the interpreter unwinds the stack looking for exception handlers before finding that there is none? In other languages/VMs such as SBCL the runtime can look up the stack for handlers, and invoke the debugger before destructively unwinding.

[mathisfun123]

The other guy up above claims this is a feature unique to calling functions, rather than all error states, and that the lisp runtime specifically guards against this. If that's the case then my answer is very simple: it would be trivial to guard function calls (all function calls) to achieve the exact same functionality in python. I'm in bed but it would literally take me 5 minutes (I would hook eval of the CALL_FUNCTION opcode). Now it would be asinine because it's a six-sigma event that I call a function that isn't defined. On the other hand, setting a breakpoint and redefining functions as you go works perfectly well and is the common case and simultaneously the kind of "repl driven development" discussed all up and down this thread.

[versteegen]

Thank you, you're very helpful despite this raging flame war. I'm glad to hear you can hook opcodes like that, then you really can do anything. And I really need to give "set a defensive breakpoint and then step through the function" an honest go. Now that you say it, I realise I haven't.

[mathisfun123]

>I'm glad to hear you can hook opcodes like that, then you really can do anything

Just in case someone comes around calls me a liar: the way to do this is to spread the bytecodes out one per line and set a line trace. Then when your bytecode of choice pops up, do what you want (including manipulate the stack) and advance the line number (cpython let's you advance the manipulate the line number).