>>> def kwadrat(x):
...     return x*x
...
>>> d = {}
>>> d[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 1
>>> d[1] = 'abc'
>>> d[1]
'abc'
>>> d[1] = kwadrat
>>> d[1](5)
25