looking up dictionaries by values

[Sandman]

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.

[James Stroud]

See the thread from earlier today, this list (py*********@python.org).

"newbie: dictionary - howto get key value"

On Thursday 10 March 2005 06:26 pm, 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.

--
James Stroud, Ph.D.
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

[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