Make error handlers order of registration respected when handling errors

[avilaton]

Using an regular dict on error_handlers, both at Api and at Namespace, mean that which handler was not predictable. We had 2 error handlers, one for a generic service exception and one for a more specific exception that needed special care. Our registration worked some times, but not others, and this is the root cause. Here is a sample of what we had

class GenericError(Exception):
    pass


class SomeSpecificError(Exception):
    pass


ns = Namespace("some_route")

@ns.errorhandler(SomeSpecificError)
def handle_specific_error(error):
    return {"message": "something specific happened"}, 401

@ns.errorhandler(GenericError)
def handle_specific_error(error):
    return {"message": "generic error"}, 401

and a route was raising SomeSpecificError. One sees ocurrences of one or the other message depending on what is returned from the dict were those errors are stored.

[codecov]

Codecov Report

Merging #201 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #201   +/-   ##
=======================================
  Coverage   96.85%   96.85%           
=======================================
  Files          19       19           
  Lines        2705     2705           
=======================================
  Hits         2620     2620           
  Misses         85       85           

Impacted Files	Coverage Δ
flask_restx/api.py	96.69% <100.00%> (ø)
flask_restx/namespace.py	94.54% <100.00%> (ø)

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[avilaton]

Proposed fix for #202

[ziirish]

Thanks, I'll merge this one but this won't be necessary anymore in the future since python 3.7 language specification ensures that dict are now ordered.
It's actually the case in python 3.6 but this was not enforced by the language specs at the time so other python implementation such as PyPy might not implement it the same way.

[ziirish]

I'm not able to merge it right now, could you please rebase to master?

[avilaton]

I'm not able to merge it right now, could you please rebase to master?

done

[ziirish]

Thanks!

[avilaton]

Any ideas of when we could see a release come out?