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):
__metaclass__ = ABCMeta
def __init__(self, strDirConfig):
self.strDirConfig = strDirConfig
@abstractmethod
def _doStuff(self, signals):
pass
@property
@abstractmethod
def name(self):
#this property will be supplied by the inheriting classes
#individually
pass
class Base_1(Base):
__metaclass__ = ABCMeta
# this class does not provide the name property, should raise an error
def __init__(self, strDirConfig):
super(Base_1, self).__init__(strDirConfig)
def _doStuff(self, signals):
print 'Base_1 does stuff'
class C(Base_1):
@property
def name(self):
return 'class C'
if __name__ == '__main__':
b1 = Base_1('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
before @abstractmethod
Python 3.3+: (python docs):
class C(ABC):
@property
@abstractmethod
def my_abstract_property(self):
...
Python 2: (python docs)
class C(ABC):
@abstractproperty
def my_abstract_property(self):
...