looking up dictionaries by values

[Steve Holden]

Sandman wrote:
> Hi there,
>   I'm still a bit new to Python, and had a question.
> I have a dictionary that looks like:
> PWD = \
>   {
>    "root":     0,
>    "joe":     200,
>    "susan":   201,
> ..
> }
> 
>   In other words, the values are unique as well as the keys. I've run
> into a situation where I need to lookup the item by value. So given
> 201, I need to say the key is really susan.
> 
>  Is there a way to do this that does not traverse the entire dictionary
> multiple times?
> 
> Thanks.
> 
One way would be to keep two parallel dictionaries so you have both 
mappings. If necessary you could wrap this up as an object to make it 
easier to deal with.

regards
  Steve