Practice Problems with Solutions

1. Accessing Characters by Index

Problem:

Write a program that takes a string "Python" and prints:

• The first character
• The last character
• The third character

Solution:

s = "Python"

print("First character:", s[0])
print("Last character:", s[-1])
print("Third character:", s[2])

Explanation:

• s[0] accesses the first character because indexing starts at 0.
• s[-1] accesses the last character (negative index).
• s[2] gives the third character (P=0, y=1, t=2).

Output:

First character: P
Last character: n
Third character: t

2. Extracting a Substring Using Slicing

Problem:

Given "PythonProgramming", extract:

• "Python"
• "Programming"
• Reverse the entire string.

Solution:

s = "PythonProgramming"

print(s[0:6])     # 'Python'
print(s[6:])      # 'Programming'
print(s[::-1])    # reversed

Explanation:

• s[0:6] → starts at index 0, ends before 6
• s[6:] → starts from index 6 till end
• [::-1] → reverses because step = -1

3. Count the Occurrence of a Character

Problem:

Count how many times the letter 'o' appears in "Hello World".

Solution:

s = "Hello World"
count = s.count('o')
print("Occurrences of 'o':", count)

Explanation:

.count('o') counts the number of times 'o' occurs in the string.

Output:

Occurrences of 'o': 2

4. Check if a Word Exists in a Sentence

Problem:

Check if the word "Python" is present in "I am learning Python programming".

Solution:

text = "I am learning Python programming"
if "Python" in text:
    print("Yes, 'Python' is present.")
else:
    print("No, 'Python' is not present.")

Explanation:

The in operator returns True if the substring exists.

Output:

Yes, 'Python' is present.

5. Replace a Word in a String

Problem:

Replace the word "bad" with "good" in "This is a bad example".

Solution:

s = "This is a bad example"
result = s.replace("bad", "good")
print(result)

Explanation:

.replace(old, new) substitutes all occurrences of the old word with the new one.

Output:

This is a good example

6. Remove Whitespaces from Both Ends

Problem:

Remove leading and trailing spaces from " Hello World ".

Solution:

s = "   Hello World   "
clean = s.strip()
print(clean)

Explanation:

.strip() removes whitespace from both sides but not in between words.

Output:

Hello World

7. Convert Case

Problem:

Convert "python programming" into:

• All uppercase
• Title case
• Capitalize only first letter

Solution:

s = "python programming"
print(s.upper())
print(s.title())
print(s.capitalize())

Explanation:

• upper() → converts all letters to uppercase
• title() → capitalizes first letter of each word
• capitalize() → only first word gets capitalized

Output:

PYTHON PROGRAMMING
Python Programming
Python programming

8. Count Vowels in a String

Problem:

Write a program that counts how many vowels (a, e, i, o, u) are present in "Automation".

Solution:

s = "Automation".lower()
count = 0
for ch in s:
    if ch in "aeiou":
        count += 1
print("Number of vowels:", count)

Explanation:

• Convert to lowercase for uniformity.
• Loop through each character and check if it’s a vowel.
• Increment a counter when a vowel is found.

Output:

Number of vowels: 6

9. Check if String is Palindrome

Problem:

A palindrome reads the same backward as forward (e.g., "madam").
Check if a given string is a palindrome.

Solution:

s = "madam"
if s == s[::-1]:
    print("Palindrome")
else:
    print("Not a palindrome")

Explanation:

[::-1] reverses the string.
If the reversed version equals the original, it’s a palindrome.

Output:

Palindrome

10. Join a List of Words into a Sentence

Problem:

Join the list ["Python", "is", "fun"] into a single string with spaces.

Solution:

words = ["Python", "is", "fun"]
sentence = " ".join(words)
print(sentence)

Explanation:

join() combines elements of a list into a single string separated by the given character (space here).

Output:

Python is fun

11. Extract Digits from a String

Problem:

From "abc123xyz", extract only numbers.

Solution:

s = "abc123xyz"
digits = ""
for ch in s:
    if ch.isdigit():
        digits += ch
print(digits)

Explanation:

isdigit() checks if a character is a number.
We accumulate those into a new string.

Output:

123

12. Remove All Punctuation

Problem:

Remove all punctuation marks from "Hello!!! Are you fine?".

Solution:

import string

s = "Hello!!! Are you fine?"
clean = ""
for ch in s:
    if ch not in string.punctuation:
        clean += ch
print(clean)

Explanation:

string.punctuation contains all common punctuation marks.
We build a new string excluding those.

Output:

Hello Are you fine

13. Find the Longest Word in a Sentence

Problem:

Given "Python is an amazing programming language", find the longest word.

Solution:

sentence = "Python is an amazing programming language"
words = sentence.split()
longest = max(words, key=len)
print("Longest word:", longest)

Explanation:

• split() separates words.
• max() with key=len finds the word with the largest length.

Output:

Longest word: programming

14. Count Frequency of Each Character

Problem:

Count how many times each character appears in "banana".

Solution:

s = "banana"
freq = {}
for ch in s:
    freq[ch] = freq.get(ch, 0) + 1
print(freq)

Explanation:

• dict.get(ch, 0) initializes count to 0 if key doesn’t exist.
• Each time a character appears, its count increases by 1.

Output:

{'b': 1, 'a': 3, 'n': 2}

15. String Formatting Practice

Problem:

Use f-strings to print the following sentence dynamically:
“Student Alice scored 85 marks in Math.”

Solution:

name = "Alice"
score = 85
subject = "Math"
print(f"Student {name} scored {score} marks in {subject}.")

Explanation:

f-strings let you embed variables directly using {} placeholders.

Output:

Student Alice scored 85 marks in Math.

16. Replace Vowels with ‘*’

Problem:

Replace every vowel in "education" with an asterisk *.

Solution:

s = "education"
result = ""
for ch in s:
    if ch.lower() in "aeiou":
        result += "*"
    else:
        result += ch
print(result)

Explanation:

For each character, check if it’s a vowel. Replace it with * if true.

Output:

*d*c*t**n

17. Check If Two Strings are Anagrams

Problem:

Two strings are anagrams if they have the same letters in a different order.
Example: "listen" and "silent".

Solution:

s1 = "listen"
s2 = "silent"

if sorted(s1) == sorted(s2):
    print("Anagrams")
else:
    print("Not anagrams")

Explanation:

Sorting arranges letters alphabetically.
If sorted results match, the strings contain the same letters.

Output:

Anagrams

18. Display Only Unique Characters

Problem:

Print only characters that appear once in "mississippi".

Solution:

s = "mississippi"
for ch in s:
    if s.count(ch) == 1:
        print(ch, end="")

Explanation:

count(ch) returns how many times ch appears.
We print only those with count = 1.

Output:

m

19. Capitalize the First Letter of Each Word Without Using title()

Problem:

Convert "hello world this is python" → "Hello World This Is Python"

Solution:

s = "hello world this is python"
words = s.split()
result = " ".join(word[0].upper() + word[1:] for word in words)
print(result)

Explanation:

• split() divides sentence into words.
• Each word is reconstructed with first letter in uppercase.
• join() recombines them with spaces.

Output:

Hello World This Is Python

20. Reverse Each Word in a Sentence

Problem:

Input: "Python is fun"
Output: "nohtyP si nuf"

Solution:

sentence = "Python is fun"
words = sentence.split()
reversed_words = [word[::-1] for word in words]
result = " ".join(reversed_words)
print(result)

Explanation:

• Split sentence into words.
• Reverse each word individually using slicing.
• Join the reversed words with spaces.

Output:

nohtyP si nuf

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