On Wed, Jan 10, 2018 at 10:08 AM, Albert-Jan Roskam <sjeik_ap...@hotmail.com> wrote: > Hi, > > > In another thread on this list I was reminded of types.SimpleNamespace. This > is nice, but I wanted to create a bag class with constants that are > read-only. My main question is about example #3 below (example #2 just > illustrates my thought process). Is this a use case to a metaclass? Or can I > do it some other way (maybe a class decorator?). I would like to create a > metaclass that converts any non-special attributes (=not starting with '_') > into properties, if needed. That way I can specify my bag class in a very > clean way: I only specify the metaclass, and I list the attributes as normal > attrbutes, because the metaclass will convert them into properties.
You appear to be reimplementing Enum. > Why does following the line (in #3) not convert the normal attribute into a > property? > > setattr(cls, attr, property(lambda self: obj)) # incorrect! Because `cls` is `Meta`, not `MyReadOnlyConst`; `__new__` is implicitly a classmethod and `MyReadOnlyConst` doesn't actually exist yet. When `MyReadOnlyConst` is created by `type.__new__` it will be filled with the contents of `attrs`, so instead of `setattr` you want `attrs[attr] = property(...)`. But once you're past the learning exercise that this is, just use enum.Enum or collections.namedtuple :) -- Zach _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
