问题
Since Python 3.5 you can use Generics and other interesting stuff described in PEP-0484. I tried that and here's a code I have:
from typing import TypeVar, Generic, Optional
...
_T = TypeVar('T')
_S = TypeVar('S')
class Pool(Generic[_S, _T]):
def __init__(self) -> None:
self.pool = dict()
... getters and setters here...
This code works perfectly and does what is expected. Then I decided to extend this class to make some additional work. That's how I did that:
class PoolEx(Pool[_S, _T]):
ARGUMENTS = []
def __init__(self) -> None:
print("self=", self, self.__class__.__bases__)
super(PoolEx, self).__init__()
self.arguments_pool = dict()
... other code here ...
To test Pool class I created MyPool which looked like this:
class MyPool(Pool[str, Hello]):
pass
Then I put something like mypool = MyPool() and it worked fine. Once I implemented PoolEx, I've updated MyPool to this:
class MyPool(PoolEx[str, Hello]):
ARGUMENTS = ['name', 'surname']
And tried to do the same thing: mypool = MyPool(). Unfortunately I got:
self= <__main__.MyPool object at 0x1068644e0> (__main__.PoolEx[str, __main__.Hello],)
Traceback (most recent call last):
File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 170, in _run_module_as_main
"__main__", mod_spec)
File "/usr/local/Cellar/python3/3.5.0/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/Users/8bitjoey/.../utils/pool.py", line 141, in <module>
mypool = MyPool()
File "/Users/8bitjoey/.../utils/pool.py", line 52, in __init__
super(PoolEx, self).__init__()
TypeError: super(type, obj): obj must be an instance or subtype of type
As you can see, I also put self.__class__.__bases to the log. When I tried to test isinstance(self, PoolEx) and similar with issubclass, I got False. Same as super() verifications.
Is it something with my code or such classes can't have descendants? And if I still want to have PoolEx I have to use composition rather than inheritance.
来源：https://stackoverflow.com/questions/32650416/is-it-possible-to-inherit-from-class-with-generic-in-python