[Tutor] passing by reference

[Steven D'Aprano]

Vineeth Mohan wrote:
> Hi,
> 
> How are variables in python passed. By value or by referrence?  

Neither.

What makes you think that value and reference are the only two choices? 
See this Wikipedia article for a list of at least a dozen different 
argument passing techniques:

http://en.wikipedia.org/wiki/Evaluation_strategy

Three months ago I answered a similar question. You could do worse than 
read this:

http://www.mail-archive.com/tutor%40python.org/msg46612.html



> Is the following the only way to pass by reference? or is there any 
> other way

To mimic the behaviour of pass-by-reference, it is more common to pass a 
single-element list:

 >>> def modify(arg):
...     arg[0] = 23
...
 >>> var = [42]
 >>> modify(var)
 >>> assert var[0] == 23
 >>>


but using instance attributes also works.




-- 
Steven