Reading lines from one file and write into another file starting from 's'

r=open('read.txt',"r")  # open file in read mode

w=open("write.txt",'w') # open file in write mode

lines=r.readlines()

for line in lines:

    if(line[0]=='s'):    # write all lines start from 's' from read.txt to write.txt

        w.write(line)

r.close()

w.close()

2. Write first and last line of one file into another file

r=open('read.txt',"r")  # open file in read mode

w=open("write.txt",'w') # open file in write mode

lines=r.readlines()

w.write(lines[0])   # write  first line 

w.write(lines[-1])    # write  last line 

r.close()

w.close()

3. Write lines of one file into anther in reverse form

r=open('read.txt',"r")

w=open("write.txt",'w')

lines=r.readlines()

for line in lines:

    w.write(line[::-1])  # write line in reverse form

r.close()

w.close()

contents of read.txt

my name is mukesh

pgt computer Science

Contents of write.txt file

hsekum si eman ym

ecneicS retupmoc tgp

4. Write only digits from one file to another

fr=open('read.txt',"r")

fw=open("write.txt",'w')

s=fr.read()

w=s.split()

for i in w:

    for c in i:

                  if c.isdigit():  # check  character for digit

                                fw.write(c)

fr.close()

fw.close()

Contents in read.txt

pin code 160014

Mobile no 9646648307

E=mail id: mk168in@gmail.com

Contents in write.txt file

1600149646648307168

5.Writing upper,lower case characters and other  characters input by keyboard in different  files

f1=open('lower.txt',"w")

f2=open('upper.txt',"w")

f3=open('other.txt',"w")

n=int(input("How many characters you want to enter "))

for i in range(n):

      ch=input("Enter a character")

   if ch.islower():

       f1.write(ch)

      elif ch.isupper():

       f2.write(ch)

   else:

       f3.write(ch)

f1.close()

f2.close()

f3.close()