It's easier in some languages than others, but I would say the most common case is in Python (partially due to ease of dropping a REPL, partially due to lack of

It's easier in some languages than others, but I would say the most common case is in Python (partially due to ease of dropping a REPL, partially due to lack of compile-time checks). The one line of code you always should have at your disposal is: from IPython import embed; embed() Basically, if you have an error and can't figure out what's happening within a few seconds, stick that line in before the error and Python will give you a REPL to play around with. It's like GDB but way better.