Getting the name of an assignment

[Steven D'Aprano]

On Sat, 23 Dec 2006 14:38:19 -0800, Adam Atlas wrote:

> Is it possible for an object, in its __init__ method, to find out if it
> is being assigned to a variable, and if so, what that variable's name
> is? 

What should the variable name be set to if you do one of the following?


john = eric = graham = terry = Named_Instance()

some_list = [None, 1, "string", Named_Instance()]

fred = Named_Instance(); barney = fred; del fred


Name assignment is not a one-to-one operation. An object can have no name,
one name or many names. If your code assumes such a one-to-one
relationship between names and objects, it is wrong.


> I can think of some potentially ugly ways of finding out using
> sys._getframe, but if possible I'd prefer something less exotic.
> (Basically I have a class whose instances, upon being created, need a
> 'name' property, and if it's being assigned to a variable immediately,
> that variable's name would be the best value of 'name'; to make the code
> cleaner and less redundant, it would be best if it knew its own name
> upon creation, just like functions and classes do, without the code
> having to pass it its own name as a string.)

I suggest rethinking your data model, and accept that the name
attribute of an object is not necessarily the same as the name it is
bound to. 

If you still want a convenience function that names the object and binds
it to a name at the same time, try something like this:

def Make_A_Named_Instance(name, *args, **kwargs):
    globals()[name] = Named_Instance(*args, **kwargs)
    globals()[name].name = name


You might be tempted to replace globals() with locals() in the above.
Don't -- it doesn't generally work:

http://docs.python.org/lib/built-in-funcs.html


-- 
Steven.