[Python] Python 2.5 __missing__()

[Rob Hudson]

Hey, that's cool.  :)

How do you know what's going to be passed to __missing__()?  Is it 
always the same as __call__()?

-Rob

Bob Miller wrote:
> Python 2.5 allows classes derived from dict to define a
> __missing__(self, key) method.  That means that you can write a
> memoized function like this.
> 
>     >>> class MemoFibonacci(dict):
>     ...     def __missing__(self, n):
>     ...         self[n] = 1 if n < 2 else self[n - 1] + self[n - 2]
>     ...         return self[n]
>     ...     def __call__(self, n):
>     ...         return self[n]
>     ...
>     >>> fib = MemoFibonacci()
>     >>> [fib(i) for i in range(7)]
>     [1, 1, 2, 3, 5, 8, 13]
> 
> Note the gratuitous use of a conditional expression too. (-:
>