Beginning Question about Python functions, parameters...

Lie Ryan lie.1296 at gmail.com
Wed Nov 25 16:08:48 CET 2009


astral orange wrote:
> 
> As for the "class Name():" example above? Even though I haven't seen
> exactly what purpose 'self' serves

In many other programming language, self (or this, or Me) refers the the 
current class instance. In some languages, you can refer to an instance 
attribute without an explicit self, this, or Me; the name resolver will 
search in the local namespace (method-level), instance namespace 
(instance-level), class namespace (class-level), perhaps module level 
namespace (file-level), and finally global (application level).

Python interpreter is simple and stupid. It doesn't have many smarts; 
instead of having such a sophisticated name resolver, the compiler 
passes an argument to the function, making `self` a local variable that 
refers to the current instance.

Python programmers accesses instance and class namespace by explicitly 
referring to `self`; the name resolver only have two places to lookup 
names: local namespace (method level) and global namespace (module-level 
[!] not application level in python).

This choice of design simplifies the name resolver, simplifies 
method/function object design (since it does not need any code to handle 
an otherwise implicit self), and completely eliminates ambiguity (to the 
programmer) when having a local variable with the same name as an 
instance variable. Among many other advantages.

The side-effect of this design choice is self must be explicitly 
referenced to access class/instance attributes; unlike in some other 
language where self/this/Me may be omitted when it doesn't clash with 
other variable in local namespace.



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