CODEWITHSUNDEEP
pythonclass
ap0
ap0

Reputation: 1173

Class Attributes/Variables in Python

Two examples;

class Foo1:
    something = 0
    def __init__(self, n):
        self.something = n

and 

class Foo2:
    def __init__(self, n):
        self.something = n

Both classes seem to have the same behaviour:

x = Foo1(42)
y = Foo2(36)
print x.something
# will print 42
print y.something
# will print 36

But in the class Foo1 is the variable self.something (in the constructor) actually the variable something as defined at the beginning of the class? What is the difference here? Which way is preferred to use?

Upvotes: 1

Views: 105

Answers (2)

anon582847382
anon582847382

Reputation: 20351

something is not the same as self.something. When you access x.something or y.something, you are accessing the version that is bound to that instance. The original something is local to that type rather than an object from that type:

>>> Foo1.something
0
>>> Foo1(42).something
42

Upvotes: 2

Tamim Shahriar
Tamim Shahriar

Reputation: 739

The difference is, in the first case, you can access the data attribute without using an object (or instance). In the second case, you can't. Please check the following code snippet :

>>> class Foo1:
...     something = 0
...     def __init__(self, n):
...         self.something = n
... 
>>> Foo1.something
0
>>> class Foo2:
...     def __init__(self, n):
...         self.something = n
... 
>>> Foo2.something
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: class Foo2 has no attribute 'something'
>>>

Hope I could clarify. For more, please read this : https://docs.python.org/2/tutorial/classes.html#class-and-instance-variables

Upvotes: 3

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