Added metrics to MetricFamily exceptions to fix #362

[wolph]

No description provided.

[brian-brazil]

That's a bit more code than I'd expect. We can't use raise from as we support 2.6/7, but https://stackoverflow.com/questions/9157210/how-do-i-raise-the-same-exception-with-a-custom-message-in-python/9157277 should work.

[wolph]

That's indeed possible, but the added advantage of this method is that you can catch MetricErrorBase and can be certain it has a metric property :)
Additionally, testing is a bit easier like this and it still works if you're simply trying to catch something like TypeError.

[brian-brazil]

We already know what the metric is, as it's in local scope.

[wolph]

Only from within the exposition method, which is what I was trying to mitigate here. This allows for easy exception handling outside of it while still maintaining full backwards compatibility.

Can you provide an example of how you would prefer the handling otherwise? The question you linked has 11 answers so that's a little broad :P

[brian-brazil]

First answer, 2nd example.

[wolph]

I've simplified it a bit now, is that better?

[brian-brazil]

This code should also go in the openmetrics format generator

[brian-brazil]

Thanks!