In PEP 8, Guido said that Python classes should be capitalized for everything but builtin classes:
Note that there is a separate convention for builtin names: most builtin names are single words (or two words run together), with the CapWords convention used only for exception names and builtin constants.
I'm curious: why are some builtin classes in CapWords and others not? For example, classes in the datetime modules (datetime, date, timedelta, etc.) are not capitalized. However, Request (in urllib) and Queue are.
Is there a reason or story behind this?