[Tutor] custom error classes: how many of them does one need?

[eryksun]

On Sun, Jul 7, 2013 at 2:37 PM, Albert-Jan Roskam <fomcl at yahoo.com> wrote:
> # this is a global variable (perhaps in __init__.py)
> # if warningsAsErrors > 0, even warnings will  raise an error.
> import operator
> warningsAsErrors = bool(os.getenv("warningsAsErrors"))

I'd use uppercase for the environment variable, with the application
name as a prefix, and only require that it's defined (i.e. check if
it's in os.environ).

For a library you can leave it for the user to decide how to handle warnings:

http://docs.python.org/2/library/warnings

    >>> class MyWarning(UserWarning): pass
    ...
    >>> warnings.warn('the sky is falling', MyWarning)
    __main__:1: MyWarning: the sky is falling

    >>> warnings.simplefilter('error', MyWarning)
    >>> warnings.warn('the sky is REALLY falling', MyWarning)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    __main__.MyWarning: the sky is REALLY falling

    >>> warnings.simplefilter('ignore', MyWarning)
    >>> warnings.warn('Listen! The sky is falling!', MyWarning)
    >>> # crickets

>> SpoonError
>> +-- TeaspoonError
>> +-- SoupSpoonError
>> +-- DesertSpoonError
>
> DesertSpoonError? LOL! ;-)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
SpellingError: No dessert for you!