Drop into REPL when your program crashes.

Hi,

Recently I have been increasingly adding this piece of code as
a preamble to a lot of my code.

    import (sys, os, ipdb)

    def debug_hook(exc_type, exc_value, traceback):
        if exc_type is KeyboardInterrupt:
            sys.__excepthook__(exc_type, exc_value, traceback)
            return
        print(f"Uncaught exception: {exc_type.__name__}: {exc_value}")
        ipdb.post_mortem(traceback)

    if os.environ.get('DEBUG'): sys.excepthook = debug_hook

This has been extemely helpful when debugging and even in prod. When
degugging, this helps me go up and down my backtrace like I am in gdb.
In fact, it is better than gdb. I can use evaluate any python expression
directly, and verify the shape of my tensors and exactly what caused
the error. It's like freezing the entire program right at the time the
program failed. This way I don't have to second guess what exactly
failed in the entire training loop and the next time I can fix it.

    if True or os.environ.get('DEBUG'): sys.excepthook = debug_hook

Even when not debugging, it helps me salvage the results if a 3 week
running experiment fails at 90% completion.

    Annada