DeprecationWarning

This package was available under exc on PyPI and has undergone a recent migration to meta_exc. It will no longer be available to be installed via pip install exc after 2019-06-17. Please update your codebase to use pip install meta_exc.

The exc package

The meta_exc package provides a metaclass for exceptions, allowing on-the-spot subclassing, e.g. in order to have one exception class per raise site. It is easy to use, as the following example illustrates

import meta_exc

class FruitError(meta_exc.Exception):
    pass

import sys
fruit = sys.argv[1]

try:
    if fruit in ('lemon', 'lime', 'grapefruit'):
        raise FruitError['too_sour']('%ss are too sour!' % fruit)
    elif fruit == 'jalapeno':
        raise FruitError['too_spicy']('%ss are too spicy!' % fruit)
    print("Nom nom")
except FruitError['too_sour']:
    print('I did not eat the fruit because it was too sour...')
except FruitError:
    print('I did not eat the fruit for some reason.')

There are wrapped versions of all the builtins: meta_exc.TypeError, meta_exc.IOError and so forth. The metaclass is called DerivableException.

The intended usage of meta_exc is for each exception site to raise an exception with a unique class, so that they may be caught individually.

Shorthand syntax

meta_exc.Exception['a/b'] == meta_exc.Exception.specialize('a/b') == meta_exc.Exception.specialize('a').specialize('b')

Compatibility

meta_exc should work with Python >= 2.6 and Python >= 3. It does not work in Python 2.4 because of limitations on exception types. In Python 3, try/except does not consult instancehook or subclasshook, so meta_exc.Exception cannot be used to catch plain Exception (but it can be in Python 2).