Python equivalent of pointers

Question

In python everything works by reference:

>>> a = 1
>>> d = {'a':a}
>>> d['a']
1
>>> a = 2
>>> d['a']
1

I want something like this

>>> a = 1
>>> d = {'a':magical pointer to a}
>>> d['a']
1
>>> a = 2
>>> d['a']
2

What would you substitute for magical pointer to a so that python would output what I want.

I would appreciate general solutions (not just for the above dictionary example with independent variables, but something that would work for other collections and class/instance variables)

Answer 1

What about a mutable data structure?

>>> a = mutable_structure(1)
>>> d = {'a':a}
>>> d['a']
1
>>> a.setValue(2)
>>> d['a']
2

An implementation might look like

class mutable_structure:
  def __init__(self, val):
    self.val = val

  def __repr__(self):
    return self.val

Answer 2

The standard solution is to just use a list; it's the easiest mutable structure.

a = [1]
d = {'a': a}
a[0] = 2
print d['a'][0]