Core Python Programming (2nd Edition)

In keeping with OOP tradition, Python imposes the restriction that methods cannot be invoked without
instances. An instance must be used to perform method calls. This restriction describes Python's concept
of binding, where methods must be bound (to an instance) in order to be invoked directly. Unbound
methods may also be called, but an instance object must be provided explicitly in order for the
invocation to succeed. However, regardless of binding, methods are inherently attributes of the class
they are defined in, even if they are almost always invoked via an instance. We will further explore
bound and unbound methods later in Section 13.7.
13.4.3. Determining Class Attributes
There are two ways to determine what attributes a class has. The simplest way is to use the dir() builtin
function. An alternative is to access the class dictionary attribute __dict__, one of a number of special
attributes that is common to all classes. Let us take a look at an example:
>>> class MyClass(object):
... 'MyClass class definition'
... myVersion = '1.1' # static data
... def showMyVersion(self): # method
... print MyClass.myVersion
...
Using the class defined above, let us use dir() and the special class attribute __dict__ to see this class's
attributes:
>>> dir(MyClass)
['__class__', '__delattr__', '__dict__', '__doc__',
'__getattribute__', '__hash__', '__init__', '__module__',
'__new__', '__reduce__', '__reduce_ex__', '__repr__',
'__setattr__', '__str__', '__weakref__', 'myVersion',
'showMyVersion']
>>> MyClass.__dict__
>>> print MyClass.__dict__
{'showMyVersion': ,
'__dict__': ,
'myVersion': '1.1', '__weakref__': , '__doc__':
'MyClass class definition'}
There are a few more attributes added for new-style classes as well as a more robust dir() function.
Just for comparison, here is what you would see for classic classes:
>>> dir(MyClass)
['__doc__', '__module__', 'showMyVersion', 'myVersion']
>>>
>>> MyClass.__dict__
{'__doc__': None, 'myVersion': 1, 'showMyVersion':
, '__module__':
'__main__'}