Intercepting binding?

Rhodri James rhodri at
Thu Sep 24 02:40:34 CEST 2009

On Thu, 24 Sep 2009 01:15:14 +0100, andrew cooke <andrew at> wrote:

> This is a bit vague, I'm afraid, but is there any way for me to take
> code like:
>    a = Foo()
>    beta = Bar()
> and somehow attach the string "a" to the Foo instance and "beta" to
> the Bar instance.  At some later point in the program I want to be
> able to look at the Bar instance and say to the user "this was called
> beta in your routine".

Fundamentally, not without the user's collusion.  The best you can do
if you don't have access to the right namespace dictionary is to pass
the object a name explicitly:

class Foo(object):
   def __init__(self, name): = name
     # ...and anything else

a = Foo('a')

The problem is that objects can have more than one name at a time,
and that assignment targets can be more than simple names.  What
would you want to say about:

eggs[42] = Foo()
beans['spam'] = Foo()
chips.spam = Foo()
spam[eggs.beans['chips']] = Foo()

and so on.

The thing to google for is Python's assignment model, because it's
probably not what you think it is.

Rhodri James *-* Wildebeest Herder to the Masses

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