[Tutor] fast list traversal

Shawn Milochik Shawn at milochik.com
Thu Oct 30 19:46:50 CET 2008

On Thu, Oct 30, 2008 at 2:40 PM, bob gailer <bgailer at gmail.com> wrote:
> Dinesh B Vadhia wrote:
>> I need to process a large number (> 20,000) of long and variable length
>> lists (> 5,000 elements) ie.
>>  for element in long_list:
>>    <do something with element>        # the result of this operation is
>> not a list
>>  The performance is reasonable but I wonder if there are faster Python
>> methods?

You might try using dictionaries instead. I've had phenomenal speed
gains by switching lists to dictionaries before, although that may
have had more to do with the fact that I needed to access certain
values, rather than iterating through them in sequential order like
you're doing.

It seems counter-intuitive because  a dictionary has a key and a
value, and you really only need the key (you can leave all the values
blank, or set them to zero or something), but it's a lot faster to
find a dictionary element than a list element. It has something to do
with the underlying code, but I have been assured that the same thing
applies to hashes and arrays in Perl, etc.


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