Kent's presentation introduces professional python programmers to industry standard ANSI common lisp condition system. Also good for people who picked up lisp from outside of the lisp milieu and didn't grow-up-with lisp style condition traditions.

If you wrote a new program last year, and a new data type last month, and you run the big program from last year on the new data type, the program's type checking will not recognize the type.

Instead of halting and catching fire, Pitman's condition handling adopted by lisp industry in ANSI CL gives advice in the form of new handlers without rewriting previously existing programs. A handler can accept a condition (could be a type error), resolve the condition and take a local continuation back into the running program. The resolutions can be automatic or mixed initiative.

This is an incredibly important piece of lisp thought leadership in software engineering and computer science.

In 1960, McCarthy specified that lisp should pioneer advice taking programs, and in the early 80s, Goodwin pointed out that in industry settings data types are often newer than the programs that have to use them.

"Pitman errors" are a key modern industry realization of these principles.

nhplace.com/kent/CL/
My hyperspec adapted lisp example:
screwlisp.small-web.org/fundam…
Mastodon:
gamerplus.org/@screwlisp