Does it make a difference using self for a temporary variable in a Python method?

Question

I sometimes need to use temporary variables in method definitions that aren\'t used outside the method. Is there any difference in behaviour between using self.MyVaria

Answer 1

The first creates a lasting reference on the class instance, and will be available on the object outside the scope of your method. The latter creates a purely local reference, which will not be available outside the method. Which is better depends on the situation, but if it's actually intended to only be a temporary variable use a local (non-self) variable.

Case 1:

>>> foo = MyClass()
>>> foo.MyVariable
...
AttributeError: 'MyClass' object has no attribute 'MyVariable'
>>> foo.Hello('bar')
'Hello bar'
>>> foo.MyVariable
'Hello bar'

Case 2 is as above, except that MyVariable is still not an attribute of the object after calling Hello.