[Tutor] Drifting Values in urllib.

[Danny Yoo]

On Sun, 7 May 2006, Alan Gauld wrote:

>> Am I missing something fundamental here? I am not used to dictionaries 
>> swirling around like this. :-)
>
> Caveat: I didn't read this through thoroughly but...
>
> Dictionaries are not in any specific order, you cannot rely on the order 
> remaining constant. If you are relying on the order you may well get 
> bitten, you need to extract the data in the order you need it


The appropriate data structure in this case might then be a list of 
key-value pairs.  For example, rather than:

     { 'a' : 'alpha',
       'b' : 'beta',
       'e' : 'eta' }

we can encode the same key-to-value pairing with a list of 2-tuples:

     [('a', 'alpha'),
      ('b', 'beta'),
      ('c', 'eta')]

which contains the same information content, but optimized for sequential 
ordering rather than random-access lookup.  This list will maintain the 
sequence of the items, and we'll still be able to do key-value lookups if 
we write a simple lookup() function.