How to reference a dict object?

I have a Python dict object d. d = {'a': 1, 'b': 2, 'c': 3}. My problem is really simple. I want to reference a variable to the elements of d. For example, something like:

In[1]: p = d['a']
>>> p = 1
In[2]: p = 2
In[3]: d
>>> d = {'a': 2, 'b': 2, 'c': 3}

Is that even possible? But as far as I know dict objects are mutable.