Christian Wyglendowski

I am a Network Administrator at a small college in Illinois. I began learning Python in 2002 while working as a PC Technician. It has been invaluable for systems administration and was just plain enjoyable to learn (or keep learning, I should say!).

Code Clinic

BrianvandenBroek came up with a great idea to do periodic programming problems with a group of others and then do a shared analysis afterwards to see the different approaches we all took on the problem. At this time, it is called the Python Code Clinic. Another participant who has a wiki page is ChadCrabtree.

Random Writer

Our first project was the [http://nifty.stanford.edu/2003/randomwriter/ Random Writer] from the [http://nifty.stanford.edu/ Standford Nifty projects site]. You can read more about the project at the Nifty site.

I chose to tackle the project from an object oriented perspective. I have slowy been "getting it" as far as OOP goes and this proved to be some more good practice. Here is my base class, RandomWriter <--how do I make that not link?:

import random

class RandomWriter:
    def __init__(self, seedLen, outLen, inName, outName):
        #initialize instance variables from parameters
        self.seedLen = seedLen              #seed length in characters
        self.outLen = outLen                #output file length in characters
        self.outTotal = 0                   #initialize total chars written to zero
        
        self.seed = None                    #initialize seed to None

        #open files        
        inFile = file(inName)               #open the input file
        self.outFile = file(outName, 'w')   #open the output file
        
        self.text = inFile.read()           #create string variable with contents of inFile
        inFile.close()                      #bye, inFile
        self.textLen = len(self.text)       #get the length in chars of the text to analyze
        self._selectSeed()                  #generate a seed from the text
        self.matches = []                   #iv for matches
        self.newChar = ''                   #iv for the next char from the text

        #write the initial seed to the output file
        for ch in self.seed:                
            self._writeChar(ch)
        

    def _selectSeed(self):
        """get a random seed that is self.seedLen long"""
        pos = random.randint(0, self.textLen-1)
        self.seed = self.text[pos:pos+self.seedLen]

    def _getMatches(self):
        """build a list of indexes of the current seed in the text"""
        matches = []
        match = self.text.find(self.seed)
        matches.append(match)
        while match != -1:
            match = self.text.find(self.seed, match+1)
            matches.append(match)
        return matches

    def _getSubChars(self):
        """build a list of the chars that come after our current seed in the text"""
        subChars = []
        for index in self.matches:
            if index >= 0:
                try:
                    ch = self.text[index+self.seedLen]
                except IndexError: #oops! end of the text
                    ch = self.text[-1] #get last char
                subChars.append(ch)
        return subChars

    def _writeChar(self, ch):
        """write char to output file and increment outTotal counter"""
        self.outFile.write(ch)
        self.outTotal += 1

    def _updateSeed(self, ch):
        """add the latest char to the end of the seed and drop the first char"""
        self.seed = self.seed[1:] + ch

    def Step(self):
        """process current seed, write probable subsequent char, build new seed"""
        self.matches = self._getMatches()
        subChars = self._getSubChars()
        nextChar = random.choice(subChars) #grab a "random" subsequent character
        self._writeChar(nextChar)
        #print "Wrote", nextChar
        self._updateSeed(nextChar)
        #print "New seed is", self.seed

    def Run(self):
        """do a Step for every char to be written"""
        for i in range(self.outLen - self.outTotal):
            self.Step()

Here is my implementation file:

import sys
import randomwriter

def usage():
    print "python randomwrite.py SEEDLENGTH OUTLENGTH INFILE OUTFILE"
    
    
def main():
#check for proper number of args
    if len(sys.argv) != 5:
        usage()
        sys.exit(1)        
    
    seedLength = int(sys.argv[1])
    outLength  = int(sys.argv[2])
    inFile     = sys.argv[3]
    outFile    = sys.argv[4]

#begin error checking --------------------
    if seedLength < 1 or outLength < 1:
        print "SEEDLENGTH and OUTLENGTH need to be greater than zero."
        sys.exit(1)

    try:
        rw = randomwriter.RandomWriter(seedLength, outLength, inFile, outFile)
    except IOError:
        print "Error reading or writing files.  Please double check file names and locations."
        sys.exit(1)

    if rw.seedLen > rw.textLen:
        print "The input file has to contain at least as many characters as SEEDLENGTH."
        sys.exit(1)
#end error checking ----------------------

##    print "Initial seed is", rw.seed
##    print "Processing..."
    rw.Run()

if __name__ == '__main__':
    import profile
    profile.run("main()")

Analysis

Forthcoming...

Email: MailTo(christian AT SPAMFREE dowski DOT com)

...

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