Possible Duplicate:
Instance variables vs. class variables in Python
What is the difference between these two situations and how is it treated with in Python?
Ex1
class MyClass:
anArray = {}
Ex2
class MyClass:
__init__(self):
self.anArray = {}
It seems like the in the first example the array is being treated like a static variable. How does Python treat this and what is the reason for this?
In the first example, anArray (which in Python is called a dictionary, not an array) is a class attribute. It can be accessed using MyClass.anArray. It exists as soon as the class is defined.
In the second example, anArray is an instance attribute. It can be accessed using MyClass().anArray. (But note that doing that just throws away the MyClass instance created; a more sensible example is mc = MyClass(); mc.anArray['a'] = 5.) It doesn't exist until an instance of the class is created.
It is declared diffrent area. Ex1 is Like global or static variable.
obj = MyClass()
obj2 = MyClass()
print "IS one instance ", id(obj.anArray) == id(obj2.anArray)
Ex2 is local attribute.
obj = MyClass()
obj2 = MyClass()
print "IS one instance ", id(obj.anArray) == id(obj2.anArray)
