Python dynamic attribute creation

[Steven D'Aprano]

On Thu, 01 Jul 2010 23:46:55 +0800, WANG Cong wrote:

> However, I think setattr() is a builtin function, using it exposes the
> *magic* of metaprogramming (or class-programming, if more correct) at a
> first glance.

There's nothing magic about metaprogramming.

If you're a programmer, you write programs. Some of those programs will 
be programs about text ("programming"), programs about numbers 
("programming"), programs about databases ("programming"), programs about 
staff performance data ("programming"), and programs about programs 
("metaprogramming"). But it's still just programming, and there's nothing 
magical about it. Languages that try to frighten you away from 
metaprogramming are doing you a disservice. That's like teaching an 
electrical engineer how to make all sorts of devices, but not how to make 
voltmeters or ammeters because they're "meta-electronics".

I'm pretty sure that IT is the only discipline that cares about this 
distinction between "normal work" and "meta work". Engineers are quite 
happy to make the tools they need to make the tools they need to make the 
tools they need to make something. Carpenters would think you were crazy 
if you said that building a scaffold was "meta-carpentry" and therefore 
"magic" and something to be avoided.

There's even a children's song about the sort of loops you can get into 
when you need a tool X to fix some item Y, but you need Y in order to fix 
the tool first:

http://www.songsforteaching.com/folk/theresaholeinthebucket.htm

It's only in IT that "meta work" is considered "special", and that (I 
think) is because of the influence of academia. Don't get me wrong, I'm a 
big fan of academia, but I think sometimes they need a good dose of 
reality.

Back before IT was a discipline, people used to write self-modifying code 
and programs to generate programs and other metaprogramming all the time, 
and nobody thought twice about it. Now admittedly, *some* metaprogramming 
techniques (like self-modifying code) make debugging much, much harder, 
and therefore should be avoided *for that reason*, but that's nothing to 
do with metaprogramming. If you write code with variables like:

a1649264273528924 = a1649269279528924 + a1645976427328924

that's just "programming" but it's damn near impossible to efficiently 
debug too.



-- 
Steven