Steven D'Aprano wrote: > On Fri, 26 Apr 2013 07:39:32 +0200, Peter Otten wrote: > >> A class body is basically a function body that is executed once. To >> allow an assignment >> >>>>> x = 42 >>>>> class A: >> ... x = x >> ... >> >> which is not possible inside a function > > > As far as I can tell, the documentation says that this assignment should > also be impossible inside a class. Unless I'm missing something, I think > this is a bug. > > http://docs.python.org/3/reference/executionmodel.html Will have a look. > [...] >> However, while the above gives some technical background it doesn't >> explain why this scheme was chosen. My guess is that when Python got >> closures nobody was willing to do the extra work to make class bodies >> namespace-aware. The alternative, disallowing x = x in classes, would >> have seriously broken backwards-compatibility. > > Not so. x = x was not allowed in classes before there were closures: > > > [steve@ando ~]$ python1.5 > Python 1.5.2 (#1, Aug 27 2012, 09:09:18) [GCC 4.1.2 20080704 (Red Hat > 4.1.2-52)] on linux2 > Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam >>>> >>>> >>>> def f(): > ... x = 1 > ... class Test: > ... x = x > ... return Test > ... >>>> T = f() > Traceback (innermost last): > File "<stdin>", line 1, in ? > File "<stdin>", line 3, in f > File "<stdin>", line 4, in Test > NameError: x
Define a global variable x and run it again. I don't have an ancient Python lying around but my "prediction" is >>> x = 42 >>> f().x 42 which would be the same behaviour as that of Python 3.3. -- http://mail.python.org/mailman/listinfo/python-list
