On Mon, Jul 4, 2016 at 10:41 PM, Ian Kelly <ian.g.ke...@gmail.com> wrote: > On Mon, Jul 4, 2016 at 9:20 PM, Steven D'Aprano <st...@pearwood.info> wrote: >> I got this in Python 3.6: >> >> >> py> class A: >> ... var = 999 >> ... print(var) # succeeds >> ... class B: >> ... x = var >> ... >> 999 >> Traceback (most recent call last): >> File "<stdin>", line 1, in <module> >> File "<stdin>", line 3, in A >> File "<stdin>", line 4, in B >> NameError: name 'var' is not defined >> >> >> I expected that `var` would be available during the construction of B, just >> as it was available inside A, but not to methods inside B. Obviously my >> expectations are invalid. Can anyone explain the actual behaviour? > > Class definitions don't create closures like functions do. When Python > executes a class definition, the metaclass creates a dict, and then > the interpreter execs the class body using that dict as the locals. > The body of class A has one locals dict, and the body of class B has a > completely separate locals dict. The only way to share variables > between them (prior to the class objects actually being constructed) > is via globals.
Or I suppose one could write a metaclass that does something fancy when creating the dicts. -- https://mail.python.org/mailman/listinfo/python-list
