String Manipulation in Python Class-XI

🧩 1. Introduction to Strings

Definition:
A string in Python is a sequence of characters enclosed within single quotes (' '), double quotes (" "), or triple quotes (''' ''' or """ """).
Examples: name = 'Alakshya' city = "Dehradun" paragraph = '''This is a multi-line string.'''
Strings are Immutable:
Once created, a string cannot be changed. Any modification creates a new string.

✂️ 2. String Slicing

Definition:
Slicing means extracting a portion (substring) of a string using index positions.
Syntax:string[start : end : step]
- start → index to begin (default = 0)
- end → index to stop (excluded)
- step → increment (default = 1)
Examples:

s = “PYTHON”
print(s[0:3]) # Output: PYT
print(s[2:]) # Output: THON
print(s[:4]) # Output: PYTH
print(s[::2]) # Output: PTO
print(s[::-1]) # Output: NOHTYP (reversed string)

🔢 3. String Operations

A. Concatenation (+)

Combines or joins two or more strings.

a = "Hello"
b = "World"
print(a + " " + b)   # Output: Hello World

**B. Repetition (*)**

Repeats the string multiple times.

print("Hi! " * 3)   # Output: Hi! Hi! Hi!

C. Membership Operators (`in`, `not in`)

Check whether a substring exists in another string.

s = "computer"
print("put" in s)        # True
print("Comp" not in s)   # True

🔁 4. Traversing a String Using Loops

You can use loops to access each character in a string.

Using for loop:

word = "HELLO"
for ch in word:
    print(ch)

Using while loop:

word = "HELLO"
i = 0
while i < len(word):
    print(word[i])
    i += 1

🧮 5. Built-in String Functions and Methods

Here are some commonly used string methods in Python:

Function / Method	Description	Example
`len(s)`	Returns length of string	`len("India") → 5`
`capitalize()`	Converts first character to uppercase	`"hello".capitalize() → "Hello"`
`title()`	Converts first letter of each word to uppercase	`"welcome to school".title() → "Welcome To School"`
`lower()`	Converts all characters to lowercase	`"HELLO".lower() → "hello"`
`upper()`	Converts all characters to uppercase	`"hello".upper() → "HELLO"`
`count(sub)`	Returns number of occurrences of substring	`"banana".count("a") → 3`
`find(sub)`	Returns index of first occurrence; `-1` if not found	`"python".find("t") → 2`
`index(sub)`	Like find(), but gives error if not found	`"python".index("y") → 1`
`endswith(sub)`	Checks if string ends with substring	`"hello".endswith("lo") → True`
`startswith(sub)`	Checks if string starts with substring	`"hello".startswith("he") → True`
`isalnum()`	True if all characters are letters or digits	`"abc123".isalnum() → True`
`isalpha()`	True if all characters are alphabets	`"abc".isalpha() → True`
`isdigit()`	True if all characters are digits	`"123".isdigit() → True`
`islower()`	True if all characters are lowercase	`"hello".islower() → True`
`isupper()`	True if all characters are uppercase	`"HELLO".isupper() → True`
`isspace()`	True if string contains only whitespace	`" ".isspace() → True`
`lstrip()`	Removes spaces from left	`" hello".lstrip() → "hello"`
`rstrip()`	Removes spaces from right	`"hello ".rstrip() → "hello"`
`strip()`	Removes spaces from both sides	`" hello ".strip() → "hello"`
`replace(old,new)`	Replaces substring with another	`"good morning".replace("morning","evening") → "good evening"`
`join(iterable)`	Joins elements using string as separator	`" ".join(["Python","is","fun"]) → "Python is fun"`
`partition(sep)`	Splits into 3 parts: before, separator, after	`"hello@world".partition("@") → ('hello', '@', 'world')`
`split(sep)`	Splits string into list using separator	`"a,b,c".split(",") → ['a','b','c']`

🧠 6. Summary

Strings are immutable sequences of characters.
They can be indexed, sliced, and traversed.
Operations include concatenation, repetition, and membership testing.
Python provides a rich set of built-in methods for string manipulation.

🧩 7. Sample Questions for Practice

Write a Python statement to extract “thon” from "python".
What will be the output of "HELLO".lower()?
Write a Python expression to check if "data" exists in "database".
What is the output of "apple".replace('p','b')?
Write a program to count vowels in a given string.

MCQs – Strings in Python

1. What is a string in Python?

A. A numeric data type
B. A sequence of characters
C. A Boolean value
D. A list of integers

2. What is the output of:

print("hello" + "world")

A. helloworld
B. hello world
C. hello+world
D. Error

3. Which operator is used for repetition of strings?

A. +
B. *
C. **
D. %

4. What is the output of:

print("hi" * 3)

A. hihihi
B. hi3
C. 3hi
D. Error

5. Membership operator `in` is used to:

A. Compare lengths
B. Add strings
C. Check substring presence
D. Split a string

6. What will be the output of:

s = "computer"
print(s[2:6])

A. comp
B. mput
C. pute
D. com

7. What is the result of:

s = "python"
print(s[-3:])

A. tho
B. hon
C. ton
D. Error

8. Which function returns the length of a string?

A. length()
B. size()
C. len()
D. strlen()

9. What is the output of:

print("hello".upper())

A. HELLO
B. Hello
C. hello
D. error

10. What is the output of:

print("HELLO".lower())

A. hello
B. HELLO
C. Hello
D. error

11. The function `capitalize()` converts:

A. All characters to lowercase
B. All characters to uppercase
C. First character to uppercase
D. Last character to uppercase

12. Output of:

print("india is great".title())

A. India Is Great
B. India is great
C. INDIA IS GREAT
D. india is great

13. Which method counts occurrences of a substring?

A. total()
B. count()
C. find()
D. index()

14. Output of:

print("banana".count("a"))

A. 1
B. 2
C. 3
D. 4

15. Which method returns the index of first occurrence of a substring (or -1)?

A. index()
B. find()
C. search()
D. first()

16. Which method raises an error if substring not found?

A. find()
B. index()
C. count()
D. locate()

17. Output of:

print("hello".startswith("he"))

A. True
B. False
C. None
D. Error

18. Output of:

print("world".endswith("ld"))

A. True
B. False
C. ld
D. Error

19. What does `isdigit()` check?

A. All characters are letters
B. All characters are digits
C. Only first character is digit
D. Only last character is digit

20. Output of:

print("abc123".isalnum())

A. True
B. False
C. abc
D. Error

21. Output of:

print("python".isupper())

A. True
B. False
C. python
D. PYTHON

22. Which method checks if all characters are alphabets?

A. isdigit()
B. isalpha()
C. isalnum()
D. alpha()

23. Output of:

print("   hello".lstrip())

A. hello
B. hello
C. “hello “
D. “hello” with no right spaces

24. Output of:

print("hello   ".rstrip())

A. hello
B. hello___
C. hello
D. hello with leading spaces

25. Output of:

print("   hi   ".strip())

A. hi
B. hi
C. ” hi “
D. Error

26. Which method replaces part of a string with another?

A. change()
B. replace()
C. swap()
D. update()

27. Output of:

print("hello world".replace("world", "python"))

A. hello world
B. hello python
C. python hello
D. Error

28. Output of:

print(",".join(["a", "b", "c"]))

A. abc
B. a,b,c
C. a b c
D. a; b; c

29. The method `split()` returns:

A. A tuple
B. A string
C. A list
D. A dictionary

30. Output of:

print("welcome-to-python".partition("-"))

A. (‘welcome’, ‘-‘, ‘to-python’)
B. [‘welcome’, ‘to’, ‘python’]
C. (‘welcome-to-python’, ‘-‘, ”)
D. Error

✅ ANSWER KEY

1-B
2-A
3-B
4-A
5-C
6-B
7-B
8-C
9-A
10-A
11-C
12-A
13-B
14-C
15-B
16-B
17-A
18-A
19-B
20-A
21-B
22-B
23-A
24-A
25-A
26-B
27-B
28-B
29-C
30-A