[Tutor] performance considerations

dman dsh8290@rit.edu
Mon, 3 Dec 2001 12:51:39 -0500

I'm working on a script/program to do some processing (munging) on
text files in a directory tree.  In addition, for convenience, all
non-interesting files are copied without munging.  My script, as it
stands, is quite CPU intensive so I would like to optimize it some.

In the case of copying non-interesting files, what is (generally) the
most efficient way?  It seems there is no system-level "copy" command.
Is there a better way than read each byte of the file and write it out
to the new file?  I suppose I could just create a hard link, if I am
willing to tie it down to Unix-only.  Does anyone have recommendations
on how many bytes I should read at a time?

A portion of the script generates strings by starting with 'a' and
"adding" to it.  Ie "a", "b", ..., "z", "aa", "ab", ..., "zz", "aaa".
Would it be better to use a list of one-char-strings than to modify a
single string?  Here's the code I have now (BTW, that funny-looking
"isinstance" stuff requires 2.2) (also I am certain that this is not
where most of the time is spent anyways) :

    def increment( s ) :
        Increment the string.  Recursively "carries" if needed.

        assert isinstance( s , str ) , "'s' must be a string"

        # a special case, for terminating recursion
        if s == "" :
            return "a"

        # the ordinal of the next character in succession
        next_ord = ord( s[-1] ) + 1

        # check for overflow
        if ord( 'a' ) <= next_ord <= ord( 'z' ) :
            s = s[:-1] + chr( next_ord )
        else :
            s = increment( s[:-1] ) + "a"
        return s
    # end increment()

One last question for now :
I traverse the interesting files line-by-line and check them for a
regex match, then modify the line if it matches properly.  Would it be
better (faster) to read in the whole file and treat it as a single
string?  Memory is not a problem.



It took the computational power of three Commodore 64s to fly to the moon.
It takes at least a 486 to run Windows 95.
Something is wrong here.