30.Example Programs using Strings

Remove all vowel characters from a string( university question)

vowels="AEIOUaeiou"
s=input("Enter the string...")
ns=""
for char in s:
    if char not in vowels:
        ns=ns+char
print("new string after removing vowels=",ns)

Remove characters at odd index positions from a string ( university question)

s=input("Enter the string..:")

i=0

ns=""

while i<len(s):

    if i%2==0:

        ns=ns+s[i]

    i=i+1

print("New string:",ns)

palindrome checking without reversing the string ( university question)
s=input("Enter the string...")
if s==s[::-1]:
    print("palindrome..")
else:
    print("not palindrome...")

Palindrome checking using loop

s=input("Enter the string..")

beg=0

end=len(s)-1

while beg<end:

   if s[beg]!=s[end]:

         print("Not palindrome")

         break

   beg+=1

   end-=1

else:

  print("Palindrome")

Replace all the spaces in the input string with * or if no spaces found,put $ at the start and end of the string.(university question)

s=input("Enter the string:")
s=s.replace(" ","*")
if "*" not in s:
    s="\$"+ s +"\$"
    print(s)
else:
    print(s)

Slice the string to two separate strings; one with all the characters in the odd indices and one with all characters in even indices.(university question)

s=input("enter the string:")

eps=s[0:len(s):2]

print("slice with even position characters:",eps)

ops=s[1:len(s):2]

print("slice with odd position chracters:",ops)

Binary to Decimal conversion

bitstring=input("Enter a binary number...")

decno=0
expnt=len(bitstring)-1
for bit in bitstring:
    decno=decno+int(bit)* 2 ** expnt
    expnt=expnt-1
print ("The decimal number is=", decno)

Decimal to Binary Conversion

decno=int(input("Enter the decimal number...."))
if decno==0:
    print("The binary equivalent is....0000")
else:
    binaryno=""
    while decno!=0:
        b=decno%2
        binaryno=str(b)+binaryno
        decno=decno//2
    print("The binary equivalent is....",binaryno)

Remove all occurrence of a substring from a string

s=input("enter the string..")

ss=input("enter substring to remove..")

ls=len(s) # length of the string

lss=len(ss) # length of the substring

ns="" # new string

i=0

while i<ls:

  css=s[i:lss+i] #css is the substring to be compared extracted from main string

  if css==ss:

    i=i+lss

  else:

    ns=ns+s[i]

    i=i+1

print("new string",ns)

The above program can also be written with built in function replace()

str=input("Enter string ..")

sstr=input("Enter the substring to remove..")

nstr=str.replace(sstr,"")

print("string after removing substring..",nstr)

Converting all lowercase letters into uppercase ( university question)

import string

s=input('Enter the string...')

ns=""

for c in s:

 if c in string.ascii_lowercase:

    c=chr(ord(c)-32)

 ns=ns+c

print("new string=",ns)

Swapping case ..small letters to capital letters and capital letters to small letters.

s=input('Enter the string...')

ns=""

sletter='abcdefghijklmnopqrstuvwxyz'

cletter='ABCDEFGHIJKLMNOPQRSTUVWXYZ'

for c in s:

  if c in sletter:

     c=chr(ord(c)-32)

  elif c in cletter:

    c=chr(ord(c)+32)

  ns=ns+c

print("new string=",ns)

Program to replace all occurrence of a substring with a new substring (university question)

s=input("enter string..")

ss=input("enter substring to remove..")

nss=input("enter the substring to replace....")

ls=len(s)

lss=len(ss)

ns=""

i=0

while i<ls:

  css=s[i:lss+i]

  if css==ss:

     ns=ns+nss

     i=i+lss

  else:

     ns=ns+s[i]

     i=i+1

print("new string",ns)

Reversing the first and second half of a string separately ( university question)

s=input("Enter the string..:")

l=len(s)

fs=s[0:l//2]

ss=s[l//2:]

fs=fs[::-1]

ss=ss[::-1]

s=fs+ss

print("New string after reversal:::",s)

Encrypt a string using the shift cipher( key=3 Ceaser cipher)

import string
plaintxt=input("enter plain text in small letters..")
k=int(input("Enter the key...."))
s=string.ascii_lowercase
ciphertxt=""

for c in plaintxt:
    i=s.find(c)
    if i!=-1:
        ni=(i+k) % 26
        ciphertxt=ciphertxt+s[ni]
    else:
        ciphertxt=ciphertxt+c
print("cipher text...",ciphertxt)

Write a Python program to check the validity of a password given by the

user.

The Password should satisfy the following criteria:

1. Contains at least one letter between a and z

2. Contains at least one number between 0 and 9

3. Contains at least one letter between A and Z

4. Contains at least one special character from $, #, @

Minimum length of password: 6

import getpass

dig='0123456789'

cl="ABCDEFGHIJKLMNOPQRSTUVWXYZ"

sl="abcdefghijklmnopqrstuvwxyz"

sc="$#@"

flag1=0;flag2=0;flag3=0;flag4=0;flag5=0

password=getpass.getpass()

if len(password)>=6:

    flag5=1

for c in password:

        if c in dig:

            flag2=1

        if c in sl:

            flag1=1

        if c in cl:

            flag3=1

        if c in sc:

            flag4=1

if flag1 and flag2 and flag3 and flag4 and flag5:

    print("Strong password")

else:

    print("Invalid password")

  

Write Python program to count the total number of vowels, consonants, digits and blanks in a string.(university question)

s = input('Enter the string:')
s = s.lower()
vowels = "aeiou"
consonants = "bcdfghjklmnpqrstvwxyz"
digits = "1234567890"
space = " "
c = 0
v = 0
d = 0
ws = 0
for i in s:
    if i in vowels:
        v+=1
    elif i in consonants:
        c+=1
    elif i in digits:
        d+=1
    elif i in space:
        ws+=1
print("Consonents={},Vowels={},Digits={},Spaces={}".format(c,v,d,ws))

Note: you can do this program using library functions

Count number of letters , digits, words,uppercase and lower case letters in a string

num_letters = 0

num_digits = 0

num_words = 0

num_uppercase = 0

num_lowercase = 0

input_string = input("Enter a string: ")

for char in input_string:

    if char.isalpha():

        num_letters += 1

    if char.islower():

        num_lowercase += 1

    elif char.isupper():

         num_uppercase += 1

    elif char.isdigit():

        num_digits += 1

# Count words

words = input_string.split()

num_words = len(words)

    

print("Number of letters:", num_letters)

print("Number of digits:", num_digits)

print("Number of words:", num_words)

print("Number of uppercase letters:",num_uppercase)

print("Number of lowercase letters:",num_lowercase)

Assume that the variable data refers to the string "Python rules!". Use a string method to perform the following tasks: ( University Question)

a. Obtain a list of the words in the string.

b. Convert the string to uppercase.

c. Locate the position of the string "rules" .

d. Replace the exclamation point with a question mark.

data="Python rules!"

words=data.split(" ")

for w in words:

    print(w)

    

data=data.upper()

print(data)

pos=data.index('rules')

print(pos)

data=data.replace('!','?')

print(data)

Write a Python program to get a string and change all occurrences of its first character to '$', except the first character itself.(university question)

Example:onion  will change to oni$n.

def change_first_char_occurrences(input_string):

    # Check if the string is not empty

    if input_string:

        first_char = input_string[0]

        # Replace all occurrences of the first character (excluding the first one) with '$'

        modified_string = first_char + input_string[1:].replace(first_char, '$')

        return modified_string

    return input_string  # Return the original string if it's empty

# Get input from the user

user_input = input("Enter a string: ")

# Call the function and print the result

result = change_first_char_occurrences(user_input)

print("Modified string:", result)

Output:

Enter a string: onion

Modified string: oni$n