Kay Schluehr wrote: >> The enumerations specified in this PEP are instances of an ``enum`` >> type. Some alternative designs implement each enumeration as its own >> class, and a metaclass to define common properties of all >> enumerations. >> >> One motivation for having a class (rather than an instance) for each >> enumeration is to allow subclasses of enumerations, extending and >> altering an existing enumeration. A class, though, implies that >> instances of that class will be created; it is difficult to imagine >> what it means to have separate instances of a "days of the week" >> class, where each instance contains all days. This usually leads to >> having each class follow the Singleton pattern, further complicating >> the design. >> >> In contrast, this PEP specifies enumerations that are not expected to >> be extended or modified. It is, of course, possible to create a new >> enumeration from the string values of an existing one, or even >> subclass the ``enum`` type if desired. > > Maybe a metaclass implementation complicates design, but usage is > quite simple and flexible. The classics is already referenced by the > Python docs: > > http://www.python.org/doc/essays/metaclasses/Enum.py
Agreed. Allowing subclassing of an existing enum is a strong plus to me. -- Giovanni Bajo -- http://mail.python.org/mailman/listinfo/python-list
