> \w already includes both \d and _, so (unless you really want to be
> explicit about it) they are redundant. [snip]
I just started from the previous list and turned it into a regex.  Eliminating redundancy sounds good, I’ll use your version.

> Also keep in mind that they match non-ASCII letters/numbers on
> Python 3.
This was not covered by the previous tests, but I think it’s fine: the shell is concerned about some metacharacters and spaces, not Unicode letters.  To be 100% sure, I will add tests with Unicode characters for pipes.quote in 3.2, and when merging with 3.3 I’ll know if the new code still complies.