My Python application contains many abstract classes and implementations. For example:

import abc
import datetimeclass MessageDisplay(object):__metaclass__ = abc.ABCMeta@abc.abstractpropertydef display(self, message):passclass FriendlyMessageDisplay(MessageDisplay):def greet(self):hour = datetime.datetime.now().timetuple().tm_hourif hour < 7:raise Exception("Cannot greet while asleep.")elif hour < 12:self.display("Good morning!")elif hour < 18:self.display("Good afternoon!")elif hour < 20:self.display("Good evening!")else:self.display("Good night.")class FriendlyMessagePrinter(FriendlyMessageDisplay):def display(self, message):print(message)

FriendlyMessagePrinter is a concrete class that we can use...

FriendlyMessagePrinter().greet()

Good night.

...but MessageDisplay and FriendlyMessageDisplay are abstract classes and attempting to instantiate one would result in an error:

TypeError: Can't instantiate abstract class MessageDisplay with abstract methods say

How can I check if a given class object is an (uninstantiatable) abstract class?

import inspect
print(inspect.isabstract(object))                  # False
print(inspect.isabstract(MessageDisplay))          # True
print(inspect.isabstract(FriendlyMessageDisplay))  # True
print(inspect.isabstract(FriendlyMessagePrinter))  # False

This checks that the internal flag TPFLAGS_IS_ABSTRACT is set in the class object, so it can't be fooled as easily as your implementation:

class Fake:__abstractmethods__ = 'bluh'print(is_abstract(Fake), inspect.isabstract(Fake)) # True, False