Preventing a class from direct instantiation in Python

Question

I have a super class with a method that calls other methods that are only defined in its sub classes. That\'s why, when I create an instance of my super class and call its m

Answer 1

This is what I might do:

class SuperClass(object):
    def __init__(self):
        if type(self) == SuperClass:
            raise Exception(" must be subclassed.")
        # assert(type(self) == SuperClass)

class SubClass(SuperClass):
    def __init__(self):
        SuperClass.__init__(self)

subC = SubClassOne()
supC = SuperClass() # This line should throw an exception

When run (exception is thrown!):

[ 18:32 jon@hozbox ~/so/python ]$ ./preventing-direct-instantiation.py
Traceback (most recent call last):
  File "./preventing-direct-instantiation.py", line 15, in 
    supC = SuperClass()
  File "./preventing-direct-instantiation.py", line 7, in __init__
    raise Exception(" must be subclassed.")
Exception:  must be subclassed.

---

Edit (from comments):

[ 20:13 jon@hozbox ~/SO/python ]$ cat preventing-direct-instantiation.py 
#!/usr/bin/python

class SuperClass(object):
    def __init__(self):
        if type(self) == SuperClass:
            raise Exception(" must be subclassed.")

class SubClassOne(SuperClass):
    def __init__(self):
        SuperClass.__init__(self)

class SubSubClass(SubClassOne):
    def __init__(self):
        SubClassOne.__init__(self)

class SubClassTwo(SubClassOne, SuperClass):
    def __init__(self):
        SubClassOne.__init__(self)
        SuperClass.__init__(self)

subC = SubClassOne()

try:
    supC = SuperClass()
except Exception, e:
    print "FAILED: supC = SuperClass() - %s" % e
else:
    print "SUCCESS: supC = SuperClass()"

try:
    subSubC = SubSubClass()
except Exception, e:
    print "FAILED: subSubC = SubSubClass() - %s" % e
else:
    print "SUCCESS: subSubC = SubSubClass()"

try:
    subC2 = SubClassTwo()
except Exception, e:
    print "FAILED: subC2 = SubClassTwo() - %s" % e
else:
    print "SUCCESS: subC2 = SubClassTwo()"

Prints:

[ 20:12 jon@hozbox ~/SO/python ]$ ./preventing-direct-instantiation.py 
FAILED: supC = SuperClass() -  must be subclassed.
SUCCESS: subSubC = SubSubClass()
SUCCESS: subC2 = SubClassTwo()