Am 10.04.2013 11:52, schrieb Peter Otten:
Ulrich Eckhardt wrote:
[...]
It looks like this particular invocation relies on class attribute and
function __name__ being identical.
Please file a bug report.
Thanks for confirming this and reducing the test case even more.
Now, concerning Python 3, it fails to detect any test case at all! My
guess is that the unittest library was changed to use metaclasses itself
in order to detect classes derived from unittest.TestCase. Therefore,
overriding the metaclass breaks test case discovery. My question in that
context is how do I extend metaclasses instead of overriding it? In
other words, what is the equivalent to super() for class creation?
Python 3 does not recognize the __metaclass__ attribute as the metaclass.
You need to provide it like so:
def __metaclass__(name, bases, dict):
...
class X(unittest.TestCase, metaclass=__metaclass__):
pass
:|
Doing some research[0, 1] on metaclasses in 2 and 3, I have a few more
questions...
The first thing I was wondering was why Python doesn't complain about a
class property that is marked as special (leading and trailing double
underscores) but that it knows nothing about. Worse, Python 3 should be
aware of its legacy and recognize the Python 2 metaclass syntax, even if
only to reject it loudly. I'm pretty sure there is a reason for that,
The second question that came up was if there is a way to keep a
metaclass defined inside the class or if the only way is to provide it
externally. The reason I like this in-class definition is that for my
case of autogenerated test functions, everything is in one place which
used to be in a loop that modified the class after its creation. Maybe
I'm just too brainwashed by static languages though.
To get the Python2 feeling back, I have a hack in mind that involves
creating a baseclass which in turn provides a metaclass that invokes a
specific function to post-initialize the class, similar to the way
Python 2 does it automatically, but I'm wondering if there isn't
anything better. Also PEP 3115 "Metaclasses in Python 3000"[2] seems to
consider postprocessing of a class definition as better handled by a
class decorator, which is something I haven't looked at yet.
Greetings from Hamburg!
Uli
[0] http://mikewatkins.ca/2008/11/29/python-2-and-3-metaclasses/
[1] http://www.artima.com/weblogs/viewpost.jsp?thread=236234
[2] http://www.python.org/dev/peps/pep-3115/
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