python: What happens when class attribute, instance attribute, and method all have the same name?

Question

How does python differentiate a class attribute, instance attribute, and method when the names are the same?

class Exam(object):      test = "class var"      def __init__(self, n):         self.test = n      def test(self):         print "method : ",self.test  test_o = Exam("Fine")  print dir(test_o)  print Exam.test print test_o.test test_o.test() 

Output :

['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__',    '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'test'] <unbound method load.test> Fine Traceback (most recent call last):   File "example.py", line 32, in <module>     test_o.test() TypeError: 'str' object is not callable 

How to call

1. class attribute, Exam.test --> <unbound method load.test> output shows method
2. instance attribute test_o.test --> "Fine"
3. method test_o.test() --> TypeError: 'str' object is not callable

Answer 1

Class attributes are accessible through the class:

YourClass.clsattribute 

or through the instance (if the instance has not overwritten the class attribute):

instance.clsattribute 

Methods, as stated by ecatmur in his answer, are descriptors and are set as class attributes.

If you access a method through the instance, then the instance is passed as the self parameter to the descriptor. If you want to call a method from the class, then you must explicitly pass an instance as the first argument. So these are equivalent:

instance.method() MyClass.method(instance) 

Using the same name for an instance attribute and a method will make the method hidden via the instance, but the method is still available via the class:

#python3 >>> class C: ...     def __init__(self): ...         self.a = 1 ...     def a(self): ...         print('hello') ...  >>> C.a <function a at 0x7f2c46ce3c88> >>> instance = C() >>> instance.a 1 >>> C.a(instance) hello 

Conclusion: do not give the same name to instance attributes and methods. I avoid this by giving meaningful names. Methods are actions, so I usually use verbs or sentences for them. Attributes are data, so I use nouns/adjectives for them, and this avoids using the same names for both methods and attributes.

Note that you simply cannot have a class attribute with the same name as a method, because the method would completely override it (in the end, methods are just class attributes that are callable and that automatically receive an instance of the class as first attribute).