[Python-Dev] LinkedHashSet/LinkedHashMap equivalents

John Williams jrw at pobox.com
Thu Mar 10 00:14:35 CET 2005

Steven Bethard wrote:

 > Thomas Heller <theller at python.net> wrote:
 >> [About an ordered dictionary]
 > Well, that was basically the question I posed.  So far I've seen only
 > one use for it, and that one is better served by adding a function to
 > itertools.  What use do you have for it other than filtering
 > duplicates from a list while retaining order?
 > Steve

Using a LinkedHashMap generally cuts down in the amount of apparent 
randomness in a program.  This is especially helpful when it comes time 
to debug a really complicated program by diffing log files, since it 
prevents slightly different maps from having wildly different iteration 
orders.  Often using a plain HashMap can introduce enough randomness to 
make two otherwise similar log files nearly impossible to compare.

The other use case I have is for dealing with data where the iteration 
order doesn't matter to the program but it does matter to users.  For 
instance, consider the ConfigParser's write method.  Any ordering of 
values in the output is functionally equivalent, but the original data 
is likely to have come from a file that was arranged in some meaningful 
order, and it would be nice to preserve that order, especially if it can 
be done with no extra effort.


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