Support for parsing of string interval definitions

[ljanyst]

As a user, I want to be able to specify an interval definition as a string. This pull request implements this functionality. It parses the input string and calls the appropriate properties and functions. It slightly abuses asserts but you did not define any custom exceptions and I wanted to follow your style.

This is how it works:

schedule.when('every wednesday at 13:15').do(job)
schedule.when('every 15 seconds').do(job)

[coveralls]

Coverage decreased (-1.09%) to 98.905% when pulling ac33fd2 on ljanyst:interval-definitions into b4ac8ca on dbader:master.

[coveralls]

Coverage decreased (-0.4%) to 99.635% when pulling 4aa3b77 on ljanyst:interval-definitions into b4ac8ca on dbader:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 10a1edb on ljanyst:interval-definitions into b4ac8ca on dbader:master.

[ljanyst]

Perhaps it would be better to use the Scheduler.__call__ method instead of when and a ValueError exceptions instead of these assertions. Let me know what you think and I will update the code.

[coveralls]

Coverage decreased (-0.4%) to 99.638% when pulling ac6db85 on ljanyst:interval-definitions into b4ac8ca on dbader:master.

[coveralls]

Coverage decreased (-0.4%) to 99.638% when pulling ac6db85 on ljanyst:interval-definitions into b4ac8ca on dbader:master.

[coveralls]

Coverage decreased (-0.7%) to 99.275% when pulling 0d08f59 on ljanyst:interval-definitions into b4ac8ca on dbader:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 0d08f59 on ljanyst:interval-definitions into b4ac8ca on dbader:master.

[ljanyst]

Are there any chances of getting this merged? I would very much appreciate your feedback. Thanks!

[jcnaud]

Great feature. I actually use it but i also wait this merge.

[ljanyst]

Yeah, I know. ;) I needed it for this: https://github.com/ljanyst/scrapy-do but pretty useful in general.

[SijmenHuizenga]

I'm very hesitant to go forward with this.

You are proposing to add a new syntax to define a job interval as a string. This already exists: cron. If you want to encode a scheduling interval as a string (could be in a file, via an api or somewhere else) I would recommend to use the cron syntax. It is widely supported and interpretes exist in many languages (like python).

Schedule is a simple Python job scheduler. It does not support advanced features like job persistence or string parsing because other tools already do this a lot better. This library is for projects that do not need all the advanced features that APSchedule offers. The feature you are proposing is one of those advanced features that APSchedule supports, and this library won't. See CronTrigger.from_crontab().

There are for sure projects out there where encoding a job definition as a more human readable string is required, and the code you wrote seems like a good implementation. I encourage you to publish it in your own repository, add an readme with proper documentation. You could do this as a fork of this project, or even better, create a standalone library that parses strings into schedule Job instances that can be used with this scheduler. If you go this route we can definitely add a FAQ item to this library's docs pointing to your library.

[ljanyst]

That's certainly your choice. If I wanted cron I would have used cron.