Daniel Nogradi wrote: > I used to have the following code to collect all (old style) class > names defined in the current module to a list called reg: > > > def meta( reg ): > def _meta( name, bases, dictionary ): > reg.append( name ) > return _meta > > reg = [ ] > __metaclass__ = meta( reg ) > > class c1: > pass > > class c2: > pass > > print reg
That code does not create classes. Here's a slightly simplified version: >> reg = [] >>> def __metaclass__(name, bases, dict): ... reg.append(name) ... >>> class A: pass ... >>> reg ['A'] >>> A is None True # oops! > This would correctly print [ 'c1', 'c2' ]. Now I would like to switch > to new style classes but replacing class c1: and class c2: by class > c1(object): and class c2(object): doesn't work because the metaclass > associated with object will be called and not mine. Of course if I > would add __metaclass__ = meta(reg) to all class definitions that > would work, but how do I do this on the module level? If present, __metaclass__ serves as a factory for classes without an explicit base class. For example, __metaclass__ = type would turn c1 and c2 into newstyle classes (that inherit from object). If you want side effects you can wrap the metaclass into a function: >>> reg = [] >>> def __metaclass__(name, bases, dict): ... reg.append(name) ... return type(name, bases, dict) ... >>> class A: pass ... >>> class B: pass ... >>> reg ['A', 'B'] >>> issubclass(A, object) True Peter -- http://mail.python.org/mailman/listinfo/python-list
