add --dump-regexps option to print the regular expressions used to match supported sites

[chocolateboy]

I use youtube-dl as an optional downloader in a project where I don't have the luxury of invoking it on every URL to see if a site is supported. Instead, I keep a static list of the regexes used to match supported sites and manually update it by hand (well, by script and hand) periodically. Obviously this is fragile.

This patch allows youtube-dl to dump these regexes so I don't have to scrape them. Maybe someone else will find it useful.

[chocolateboy]

P.S. Yes, I agree to release it (and any other contributions) to the public domain. And, if you apply it, perhaps this option and --dump-user-agent should be placed under a "Developer Options" heading so they don't clutter up the main options.

[rg3]

I don't oppose such an option strongly, but at this moment I prefer not to implement this feature. Right now this depends on _VALID_URL, which is an internal field used for convenience and people include it when they write an InfoExtractor because they copy what they see in other InfoExtractors. Many times, however, I've been thinking about splitting a complex regexp into several ones, and modifying the "suitable()" method accordingly to check each one in turn. Moreover, "suitable()" may not depend on regular expressions at all, and just check the URL starts with a given string, for example.

I know currently the code you have implemented is small and works, yet I still think it exposes an internal implementation decision for InfoExtractors that shouldn't be exposed to users, sorry.

[chocolateboy]

That's what I thought you'd say. Oh well, worth a shot :-)

[rg3]

:)