class declaration shortcut

[Steven D'Aprano]

On Thu, 01 Mar 2007 10:44:48 +0100, Bjoern Schliessmann wrote:

> Mh. I suspect there's also more to it than I see now, but this
> __name__ seems quite useless to me. What if I rebind the class'
> name after definition? Or is it really just for some manual
> introspection? If it is, it seems a bit of an overkill to me.

Overkill? Storage of a single attribute holding a (usually short) string
is overkill?

The thing to remember is that the link between names and objects in
Python is one-way only. Names (by definition) have to know which object
they are bound to. But objects don't know what name, or names, (if any)
are bound to themselves. Yes, they *could* keep a list of the names bound
to them, but that would be a lot of work at runtime for little benefit.

So if you rebind a name, the objects can't tell. And generally you
wouldn't want them to. Something like the following is rightfully quite
rare:

>>> int
<type 'int'>
>>> int.__name__
'int'
>>> foo = int; int = "something else"
>>> type(0)    # Do you expect <type 'foo'>?
<type 'int'>
>>> int
'something else'

Normally the reason for rebinding classes, functions etc. are (1) to save
typing and (2) an optimization to save name look-ups. 

# slow way
for item in sequence:
    package.module.function(item)

# faster way
f = package.module.function
for item in sequence:
    f(item)

When you do that, you wouldn't expect the __name__ of some.module.function
to change to f, and it doesn't.

The downside is that on the rare corner case where you do want the
__name__ of an object to change, it doesn't.



-- 
Steven D'Aprano