Why does the meta class change the way issubclass () works?

Question

OK, so I write a framework that looks for python files in subdirectories with a name task.py, and then looks for classes that are derived from the base class Taskand compile them. I decided that I needed to add a meta class to Task, but then issubclass()began to behave in a strange way. Here's what the catalog layout looks like:

start.py                
tasks/__init__.py
tasks/base.py
tasks/sub/__init__.py   # empty
tasks/sub/task.py

start.py:

#!/usr/bin/env python
from tasks.base import Task1, Task2
from tasks.sub.task import SubTask1, SubTask2

print "Normal import:"
print "is SubTask1 sub class of Task1? %s" % issubclass(SubTask1, Task1)
print "is SubTask2 sub class of Task2? %s" % issubclass(SubTask2, Task2)

from tasks import setup
print "Imp import:"
setup()

Tasks / INIT .py

import os.path, imp, types
from tasks.base import Task1, Task2

# Find all task definitions
ALL_TASK1 = { }
ALL_TASK2 = { }
def _append_class(d, task, base):
    if (type(task) == types.TypeType) and issubclass(task, base):
        if task == base:
            return
        if not task.name in d:
            d[task.name] = task

this_dir = os.path.dirname(os.path.abspath(__file__))
for root, dirs, files in os.walk(this_dir):
    if not "task.py" in files:
        continue
    mod_name = "task"
    f, pathname, description = imp.find_module(mod_name, [ root ])
    m = imp.load_module(mod_name, f, pathname, description)
    f.close()

    for task in m.__dict__.itervalues():
        _append_class(ALL_TASK1, task, Task1)
        _append_class(ALL_TASK2, task, Task2)

def setup():
    print "All Task1: %s" % ALL_TASK1
    print "All Task2: %s" % ALL_TASK2

Tasks / base.py

class MetaClass (type):
    def __init__(cls, name, bases, attrs):
        pass

class Base (object): 
    __metaclass__ = MetaClass

    def method_using_metaclass_stuff(self):
        pass

class Task1 (Base):
    pass

class Task2 (object):
    pass 

Tasks / sub / task.py

from tasks.base import Task1, Task2

class SubTask1 (Task1): # Derived from the __metaclass__ class
    name = "subtask1"

class SubTask2 (Task2):
    name = "subtask2"

When I run setup.py, I got the following output (ALL_TASK1 dict is empty!):

Normal import:
is SubTask1 sub class of Task1? True
is SubTask2 sub class of Task2? True
Imp import:
All Task1: {}
All Task2: {'subtask2': <class 'task.SubTask2'>}

But when I comment out the line __metaclass__in the class Base( Task1base class), I got the expected result (ALL_TASK1 dict is not empty):

Normal import:
is SubTask1 sub class of Task1? True
is SubTask2 sub class of Task2? True
Imp import:
All Task1: {'subtask1': <class 'task.SubTask1'>}
All Task2: {'subtask2': <class 'task.SubTask2'>}

, issubclass(), imp, , import.

- ( python 2.6.1)?

Answer 1

.

>>> from tasks.base import Task1
>>> type(Task1)
<class 'tasks.base.MetaClass'>
>>> from types import TypeType
>>> type(Task1) == TypeType
False
>>> issubclass(type(Task1), TypeType)
True
>>> 

( ), TypeType, tasks.base.MetaClass. TypeType, .

def _append_class(d, task, base):
    if (issubclass(type(task), types.TypeType) and issubclass(task, base):

, , . (, , , , , -), , TypeType.

Answer 2

__metaclass__ Base, type(Base) tasks.base.MetaClass, types.TypeType.

, _append_class , , - , .

if (type(task) == types.TypeType) and issubclass(task, base):

issubclass(task,base) :

try: isbase=issubclass(task, base)
except TypeError: isbase=False
if isbase: