How can a function find the function that called it?

[kj]

I want to implement a frozen and ordered dict.

I thought I'd implement it as a subclass of collections.OrderedDict
that prohibits all modifications to the dictionary after it has
been initialized.

In particular, calling this frozen subclass's update method should,
in general, trigger an exception ("object is not mutable").

But OrderedDict's functionality *requires* that its __init__ be
run, and this __init__, in turn, does part of its initialization
by calling the update method.

Therefore, the update method of the new subclass needs to be able
to identify the calling function in order to make a special allowance
for calls coming from OrderedDict.__init__.  (Better yet, it should
be able to allow calls coming from its own class's __init__, via
OrderedDict.__init__.)

The best I've been able to do is to use inspect to get the name of
the calling function.  For the case I'm trying to identify, this
name is simply "__init__".

But Python code is awash in __init__'s... 

Is it possible to achieve a more precise identification?  Specifically,
I want to know the *class* (not the file) where this '__init__' is
defined.

(BTW, I don't understand why inspect doesn't provide something as
basic as the *class* that the method belongs to, whenever applicable.
I imagine there's a good reason for this coyness, but I can't figure
it out.)

TIA!

~kj