tracking variable value changes

[Catherine Moroney]

Hello,

Is there a way to create a C-style pointer in (pure) Python so the 
following code will reflect the changes to the variable "a" in the
dictionary "x"?

For example:

 >>> a = 1.0
 >>> b = 2.0
 >>> x = {"a":a, "b":b}
 >>> x
{'a': 1.0, 'b': 2.0}
 >>> a = 100.0
 >>> x
{'a': 1.0, 'b': 2.0}   ## at this point, I would like the value
                        ## associated with the "a" key to be 100.0
                        ## rather than 1.0

If I make "a" and "b" numpy arrays, then changes that I make to the 
values of a and b show up in the dictionary x.

My understanding is that when I redefine the value of "a", that Python
is creating a brand-new float with the value of 100.0, whereas when I 
use numpy arrays I am merely assigning a new value to the same object.

Is there some way to rewrite the code above so the change of "a" from
1.0 to 100.0 is reflected in the dictionary.  I would like to use
simple datatypes such as floats, rather than numpy arrays or classes.
I tried using weakref's, but got the error that a weak reference cannot
be created to a float.

Catherine