Question

I have a module where all classes that implement my “policies” are defined.

class Policy_Something(Policy_Base):
    slug='policy-something'
    ...

class Policy_Something_Else(Policy_Base):
    slug='policy-something-else'
    ...

I need to create a mapping from slug to class. Something like:

slug_to_class = {
    'policy-something': Policy_Something,
    'policy-something-else': Policy_Something_Else
}

I was thinking instead of automatically creating slug_to_class by inspecting the module and looking for classes that inherit from Policy_Base (similar to how unittest finds tests, I assume).

Any reason I shouldn’t do that? If not, how exactly would I do that?

Answer 1

Since your “policy” classes inherit from Policy_Base, why not import all relevant modules and then do something like this?:

import re

def slugify(s):
    return re.sub(r'\W+', '-', s.lower().replace('_', '-'))

def get_slug_to_class_items(policy_class):
    yield (slugify(policy_class.__name__), policy_class)
    for subclass in policy_class.__subclasses__():
        for slug, subclass in get_slug_to_class_items(subclass):
            yield (slug, subclass)

slug_to_class = dict(get_slug_to_class_items(Policy_Base))
# print repr(slug_to_class)

The get_slug_to_class_items function finds classes that inherit from Policy_Base (recursively iterating on the class hierarchy) and returns a generator of 2-tuples (slug, class) to be set as the items of the expected dict.

Note it’s important that all modules with “policy” classes are imported before calling get_slug_to_class_items.