56 CHAPTER4. COMPUTINGWITHSTRINGS

userfile.py

Program to createa file of usernames in batch mode.

import string

def main():
print "This programcreates a file of usernames from a"
print "file of names."

# get the filenames

infileName = raw_input("Whatfile are the names in? ")

outfileName = raw_input("Whatfile should the usernames go in? ")

# open the files

infile = open(infileName,’r’)

outfile = open(outfileName, ’w’)

# process eachline of the input file

for line in infile.readlines():

# get the firstand last names from line

first, last= string.split(line)

# create the username

uname = string.lower(first[0]+last[:7])

# write it to the outputfile

outfile.write(uname+’\n’)

# close both files

infile.close()

outfile.close()

print "Usernameshave been written to", outfileName

main()

Therearea fewthingsworthnoticinginthisprogram.I have two filesopenatthesametime,onefor
input(infile) andoneforoutput(outfile).It’s notunusualfora programtooperateonseveralfiles
simultaneously. Also,whencreatingtheusername,I usedthelowerfunctionfromthestring library.
Thisensuresthattheusernameis alllowercase,evenif theinputnamesaremixedcase.Finally, youshould
alsonoticethelinethatwritestheusernametothefile.

outfile.write(uname+’\n’)

Concatenatingthenewlinecharacteris necessaryto indicatetheendofline.Withoutthis,alloftheusernames
wouldruntogetherinonegiantline.

4.5.4 ComingAttraction:Objects

Have younoticedanythingstrangeaboutthesyntaxofthefileprocessingexamples?To applyanoperation
toa file,weusedotnotation. Forexample,toreadfrominfilewetypeinfile.read(). Thisis
differentfromthenormalfunctionapplicationthatwehave usedbefore.Afterall,totake theabsolutevalue
ofa variablex, wetypeabs(x), notx.abs().
InPython,a fileisanexampleofanobject. Objectscombinebothdataandoperationstogether. An
object’s operations,calledmethods, areinvokedusingthedotnotation. That’s whythesyntaxlooksa bit
different.