py_assignment1

#################################################################
#  my program's method to achieve the mission is by through     #
#  creating a new file --"temp.py" to record the modify results #
#  and then to delete the previous target file--"sys.py"        #
#  after that we rename the "temp.py" as "sys.py"               #
#################################################################
import os
file = open("sfs.py",'r')   #open the target file which is "sfs.py"
f = open("temp.py",'w')     #create a new file for recording the modify results
cnt=0;                      #count the lines
for line in file.readlines():
    cnt=cnt+1;
    if(cnt!=52) :
        f.write(line)
    if cnt==52 :
        line=line.strip('\n')            #delete the '\n' in order to not get to the new line
        line=line.__add__('; print( "Virus" )')#add the target string
        line=line.__add__('\n')                #add '\n'
        f.write(line)
file.close()                  #close the target file
f.close()                     #close the modify file
os.remove("sfs.py")           #delete the target file
os.rename("temp.py", "sfs.py")#rename the modify file's name as previous target file