[Tutor] Careful Dictionary Building

doug shawhan doug.shawhan at gmail.com
Fri Dec 28 17:22:51 CET 2007

I'm building a dictionary from a list with ~ 1M records.

Each record in the list is itself a list.
Each record in the list has a line number, (index 0) which I wish to use as
a dictionary key.

The problem: It is possible for two different records in the list to share
this line number. If they do, I want to append the record to the value in
the dictionary.

The obvious (lazy) method of searching for doubled lines requires building
and parsing a key list for every record. There must be a better way!

dict = {}
for record in list
    if record[0] in dict.keys():
        dict[ record[0] ].append( record )
        dict[ record[0] ] = [record]

Once you get ~ 80,000 records it starts slowing down pretty badly (I would
too ...).

Here's hoping there is a really fast, pythonic way of doing this!
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