Python-сообщество

class Newclass:
     def __init__(self, base):
        self.base = base
     def __add__(self, a):
        self.base = self.base + a
        return self.base
a = Newclass(10)
a + 20
print (a)

class Newclass:
     def __init__(self, base):
          self.base = base
     def __str__(self):
          return "%s !!! " % self.base
a = Newclass(10)
print (a)

class Newclass:
     def __init__(self, base):
        self.base = base
     def __add__(self, a):
        self.base = self.base + a
        return self.base
a = Newclass(10)
print(a + 20)
print (a)
===OUTPUT ===
30
<__main__.Newclass object at 0x986df4c>

class Newclass(int):

class Newclass():

class Newclass(object):

class ClassName():
    def __init__(self):
        pass
    # def __str__(self):
    #     return '45'
 
a = ClassName()
print (a.__str__())

andrey@ubuntu:~$ python3
Python 3.2.3 (default, Feb 27 2014, 21:33:50) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> class A():
...  pass
... 
>>> b = A()
>>> dir(b)
['__class__', '__delattr__', '__dict__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__']
>>> 
andrey@ubuntu:~$ python
Python 2.7.3 (default, Feb 27 2014, 20:00:17) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> class A():
...  pass
... 
>>> b = A()
>>> dir(b)
['__doc__', '__module__']
>>> b.__str__()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: A instance has no attribute '__str__'
>>> class C(object):
...  pass
... 
>>> d = C()
>>> dir(d)
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__']

class A:

if (a > b):
    ...