optimization question

Andrew Koenig ark at research.att.com
Sun Aug 11 13:29:57 EDT 2002

Peter> Anyway, you are optimizing before you've profiled and determined
Peter> you have a problem.


The application I'm thinking of will do lots of comparisons of the form

        s[i:j] == t

where s is very large (many megabytes), i and j are arbitrary (and might
be very far apart), and len(t) will almost always be small.  I do not want
to create a lot of large substrings, only to find out that none of them
can possibly be equal to t because they're too big.  And if I don't do
something about it in advance, it will be a real nuisance to find all of
the places where the code needs to change.

So, for example, in this case, I believe it is worth writing a function
that might look like this:

        def eqsub(s, i, j, t):
                return s[i:j] == t

and call this function everywhere instead of doing direct comparisons.
Then the optimization becomes trivial:

        def eqsub(s, i, j, t):
                return (len(t) == j-i) and s[i:j] == t

which avoids building the substrings unless necessary.

Andrew Koenig, ark at research.att.com, http://www.research.att.com/info/ark

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