Error handlers aren't working on apps

[SamuelMarks]

Here's my simple TODO app with basic error handling using your handle_errors decorator: https://gist.github.com/SamuelMarks/9d7c796b8a336bb556f3

Unfortunately it is always throwing 500s. Is there some other way I'm meant to be passing errors? E.g.: in Node.js most of my functions have the signature (err, res).

Thanks for all assistance

PS: The functions from line 103 to 110 was another attempt of mine to get exceptions handled

[twm]

Your gist doesn't even run for me:

 $ temp/bin/python todo_app.py
Traceback (most recent call last):
  File "todo_app.py", line 21, in <module>
    class CustomerStore(object):
  File "todo_app.py", line 81, in CustomerStore
    @app.handle_errors(UniqueKeyError, ValidationError)
TypeError: _f() takes exactly 3 arguments (1 given)

This is because Klein uses type checking to determine if @app.handle_errors is called with arguments or not. See

klein/klein/app.py

Line 249 in c8e74e7

if not isinstance(f_or_exception, type) or not issubclass(f_or_exception, Exception):

The problem is that your exceptions subclass BaseException instead of Exception. BaseException is only supposed to be used for "special" exceptions like StopIteration and KeyboardInterrupt that normal exception handlers shouldn't catch---see the Python docs for more information on this. Switching to subclassing Exception seems to resolve your problem.

[SamuelMarks]

Thanks

[hynek]

If either of you could contribute a chapter on error handling for the docs, that would be really amazing.

[SamuelMarks]

Sure thing: #60

[hynek]

I was more thinking of a narrative explanation how error handling works in klein. :) TBH I didn’t know about handle_errors before for example.

A complete example like #60 is useful too of course.

[SamuelMarks]

Oh right. Yeah, I'm not sure how I know about it, might've been from: https://github.com/twisted/klein/blob/master/klein/test/test_resource.py#L707

Anyway, I've updated the pull request with a new commit. So now it shows how to work with error handlers.

[hynek]

JFTR, my wish has been fulfilled with #51