Change failure mode for missing YAML parser (PyYAML) dependency

[earl]

Currently, beanstalkc for all practical purposes depends on PyYAML. Unless told otherwise, instantiating a Connection will try to import PyYAML; if that import fails, beanstalkc will log an error (using logging.error) but will continue working, by switching to a YAML-less operating mode.

I'm now convinced, that this failure mode is a mistake; it's the opposite of "fail-fast". In practice, the automatic fail-over to YAML-less operation has done more harm than good. Basically, it made (though typically brief) debugging necessary, instead of properly failing right away and making the error condition obvious.

Therefore, I plan to switch the default failure mode: in the future, when PyYAML is missing, beanstalkc won't handle the ImportError itself, but just pass it through. This is a more transparent fail-fast.

However, PyYAML won't become a hard dependency. You'll still be able to operate beanstalkc without PyYAML, explicitly switching to YAML-less operation by passing parse_yaml=False to the Connection constructor. Explicitly switching to YAML-less operation has been supported for a long time, so that's nothing new. It is already used by all real-world YAML-less deployments I know of.

So the main thing that'll change, is switching the default to a more sensible fail-fast behaviour.

Unless there is major opposition against this change, or someone suggests something better, the new default behaviour will be switched for the next feature release (beanstalkc 0.5.0).

[ptjm]

I don't have a strong opinion one way or another, but before you do it consider my recent pull request #51. That wasn't a response to this issue, but I guess it was my idea for dealing with the same problem.

[Rogdham]

:+1:

This could potentially only affect the users who do not have installed PyYAML, and still don't disable it explicitly. I would argue that they are probably not many: the logger part is set to the error level (which may not be the right level btw). This alone is pretty annoying when looking at the console during development / debug times, and quite bad during production where logs are stored, monitored, etc.

Failing shortly in that case leads to a choice being made during development, which is a good thing imho. Plus it makes beanstalkc's code cleaner, which is always nice :-)