In the following code, I create a base abstract class Base
. I want all the classes that inherit from Base
to provide the name
property, so I made this property an @abstractmethod
.
Then I created a subclass of Base
, called Base_1
, which is meant to supply some functionality, but still remain abstract. There is no name
property in Base_1
, but nevertheless python instatinates an object of that class without an error. How does one create abstract properties?
from abc import ABCMeta, abstractmethod
class Base(object):
# class Base(metaclass = ABCMeta): <- Python 3
__metaclass__ = ABCMeta
def __init__(self, str_dir_config):
self.str_dir_config = str_dir_config
@abstractmethod
def _do_stuff(self, signals):
pass
@property
@abstractmethod
def name(self):
"""This property will be supplied by the inheriting classes
individually.
"""
pass
class Base1(Base):
__metaclass__ = ABCMeta
"""This class does not provide the name property and should
raise an error.
"""
def __init__(self, str_dir_config):
super(Base1, self).__init__(str_dir_config)
# super().__init__(str_dir_config) <- Python 3
def _do_stuff(self, signals):
print "Base_1 does stuff"
# print("Base_1 does stuff") <- Python 3
class C(Base1):
@property
def name(self):
return "class C"
if __name__ == "__main__":
b1 = Base1("abc")
Since Python 3.3 a bug was fixed meaning the property()
decorator is now correctly identified as abstract when applied to an abstract method.
Note: Order matters, you have to use @property
above @abstractmethod
Python 3.3+: (python docs):
from abc import ABC, abstractmethod
class C(ABC):
@property
@abstractmethod
def my_abstract_property(self):
...
Python 2: (python docs)
from abc import ABCMeta, abstractproperty
class C:
__metaclass__ = ABCMeta
@abstractproperty
def my_abstract_property(self):
...