searching a value of a dict (each value is a list)

[Jeremy C B Nicoll]

Seongsu Lee <senux at senux.com> wrote:

> Hi,
> 
> I have a dictionary with million keys. Each value in the
> dictionary has a list with up to thousand integers.
> Follow is a simple example with 5 keys.
> 
> dict = {1: [1, 2, 3, 4, 5],
>    2: [10, 11, 12],
>    900000: [100, 101, 102, 103, 104, 105],
>    900001: [20, 21, 22],
>    999999: [15, 16, 17, 18, 19]}
> 
> I want to find out the key value which has a specific
> integer in the list of its value. For example, if I search
> 104 in the list, 900000 must be returned.

Are the integers in the lists unique?  I mean, could 104 occur in more than
one list?  If it did, would it matter which key was returned?

> How can I do this with Python? Ideas?

When I see something like this my natural response is to think that the data
structure is inappropriate for the use it's being put to.  

The code someone else posted to reverse the keys is all very well, but
surely hugely wasteful on cpu, maybe storage, and elapsed time.

Even if the dict in this form is needed for some other reason, couldn't the
code that created it also create a reverse index at the same time?

-- 
Jeremy C B Nicoll - my opinions are my own.