String Handling in Python

What is a String?

A string is text — a sequence of characters inside quotes. Strings are immutable (cannot be changed in place); any "change" creates a new string.

name = "CodingEasily"
print(name)
print(len(name))   # number of characters

Indexing & Slicing

Each character has an index starting at 0. Negative indexes count from the end.

word = "PYTHON"
print(word[0])      # first
print(word[-1])     # last
print(word[0:3])    # characters 0,1,2
print(word[::-1])   # reversed

• word[0] = first char; word[-1] = last char.
• word[0:3] = slice from 0 up to (not including) 3.
• [::-1] reverses the whole string.

Useful String Methods

Program 1: Length & Case

text = input("Enter text: ")
print("Length    :", len(text))
print("Uppercase :", text.upper())
print("Lowercase :", text.lower())
print("Title     :", text.title())

Program 2: Reverse & Palindrome Check

word = input("Enter a word: ").lower()
reversed_word = word[::-1]

if word == reversed_word:
    print(word, "is a Palindrome")
else:
    print(word, "is NOT a Palindrome")

• .lower() makes the check case-insensitive.
• word[::-1] reverses it; if it equals the original, it is a palindrome.

Program 3: Count Vowels

text = input("Enter text: ").lower()
count = 0
for ch in text:
    if ch in "aeiou":
        count += 1
print("Vowels:", count)

The loop checks each character; ch in "aeiou" is True only for vowels.

Program 4: Word Count

sentence = input("Enter a sentence: ")
words = sentence.split()
print("Total words:", len(words))
print("Words:", words)

.split() breaks the sentence at spaces into a list; len() counts the items.

Common Mistakes

• Trying to change a character: s[0] = "X" fails (strings are immutable).
• Forgetting .lower() before comparing text.
• Confusing index (position) with the character itself.

Practice Tasks

1. Ask for a name and print it in uppercase and reversed.
2. Count how many times a letter appears in a word.
3. Check if a sentence is a palindrome (ignore spaces).
4. Replace all spaces in a string with underscores.

Summary

• Strings are immutable sequences of characters; index starts at 0.
• Slicing [start:stop:step] extracts parts; [::-1] reverses.
• Common methods: upper, lower, strip, replace, split, find.