UNIT-3: Python Strings and Operators

UNIT-3: Python Strings and Operators

UNIT-3: Python Strings and Operators

3.1 Python Strings.

  • A string in Python is a sequence of characters enclosed within single ('), double ("), or triple (''' """) quotes. Strings are immutable, meaning they cannot be changed once created.

3.1.1 Multiline String, String as Character Array, Triple Quotes

Multiline Strings

Python allows multi-line strings using triple quotes (''' """).

Example:

multi_line = """This is a
multiline string in Python.
It spans multiple lines."""
print(multi_line)

String as a Character Array

Strings are arrays of characters, allowing us to access individual characters using indexing.

Example:

text = "Python"
print(text[0])  # Output: P
print(text[2])  # Output: t

Triple Quotes (''' """)

Triple quotes allow multi-line strings and are also used for docstrings.

Example:

info = '''Python is a powerful language.
It is widely used in AI and web development.'''
print(info)

3.1.2 Slicing Strings, Negative Indexing, String Length, Concatenation

Slicing Strings

Python allows extracting a part of a string using slicing.

Syntax:

string[start:end]  # Extracts substring from index 'start' to 'end-1'

Example .

text = "Python Programming"
print(text[0:6])  # Output: Python
print(text[:6])   # Output: Python (start index is 0 by default)
print(text[7:])   # Output: Programming (till end)

Negative Indexing

Negative indexing allows counting from the end of the string.

Example:

text = "Python"
print(text[-1])  # Output: n (last character)
print(text[-3:])  # Output: hon (last 3 characters)
print(text[:-3])  # Output: Pyt (everything except last 3)

Finding String Length

The len() function returns the length of a string.

Example:

text = "Python Programming"
print(len(text))  # Output: 18

String Concatenation

Strings can be joined using the + operator.
Example:
str1 = "Hello"
str2 = "World"
result = str1 + " " + str2  # Adding space manually
print(result)  # Output: Hello World

3.1.3 String Methods

Python provides several built-in string methods for string manipulation.

1. center() → Centers the string with padding

text = "Python"
print(text.center(20, "-"))  # Output: '-------Python-------'

2. count() → Counts occurrences of a substring

text = "banana"
print(text.count("a"))  # Output: 3

3. join() → Joins elements of an iterable into a string.

words = ["Hello", "Python", "World"]
print("-".join(words))  # Output: Hello-Python-World

4. len() → Returns the length of a string

text = "Python"
print(len(text))  # Output: 6

5. max() & min() → Returns the max/min character based on ASCII values

text = "apple"
print(max(text))  # Output: 'p' (highest ASCII value)
print(min(text))  # Output: 'a' (lowest ASCII value)

6. replace() → Replaces occurrences of a substring

text = "Hello World"
print(text.replace("World", "Python"))  # Output: Hello Python

7. lower() & upper() → Converts string to lowercase/uppercase

text = "Python"
print(text.lower())  # Output: python
print(text.upper())  # Output: PYTHON

8. split() → Splits a string into a list based on a delimiter

text = "apple,banana,cherry"
print(text.split(","))  # Output: ['apple', 'banana', 'cherry']

Summary Table of String Methods

3.2 Operators in Python.

  • Operators in Python are symbols used to perform operations on variables and values. Python provides several types of operators.

3.2.1 Arithmetic Operators

  • Arithmetic operators perform mathematical calculations.
Operator Description Example Output
+ Addition 5 + 3 8
- Subtraction 10 - 4 6
* Multiplication 6 * 2 12
/ Division 9 / 2 4.5
// Floor Division 9 // 2 4
% Modulus (Remainder) 9 % 2 1
** Exponentiation (Power) 2 ** 3 8 
a = 10
b = 3

print(a + b)  # Addition: 13
print(a - b)  # Subtraction: 7
print(a * b)  # Multiplication: 30
print(a / b)  # Division: 3.333...
print(a % b)  # Modulus: 1
print(a ** b) # Exponentiation: 1000 (10^3)
print(a // b) # Floor Division: 3

3.2.2 Assignment Operators

Assignment operators are used to assign values to variables.

Operator Description Example Equivalent To
= Assign value a = 10 a = 10
+= Add and assign a += 5 a = a + 5
-= Subtract and assign a -= 3 a = a - 3
*= Multiply and assign a *= 2 a = a * 2
/= Divide and assign a /= 4 a = a / 4
//= Floor divide and assign a //= 2 a = a // 2 
x = 10
x += 5  # x = x + 5
print(x)  # Output: 15

x -= 3  # x = x - 3
print(x)  # Output: 12

x *= 2  # x = x * 2
print(x)  # Output: 24

x /= 4  # x = x / 4
print(x)  # Output: 6.0

3.2.3 Comparison Operators.

  • Comparison operators compare values and return a Boolean (True or False).
Operator Description Example Output
== Equal to 5 == 5 True
!= Not equal to 5 != 3 True
> Greater than 10 > 3 True
< Less than 2 < 8 True
>= Greater than or equal to 7 >= 7 True
<= Less than or equal to 5 <= 6 True 
a = 10
b = 5

print(a == b)  # False
print(a != b)  # True
print(a > b)   # True
print(a < b)   # False
print(a >= 10) # True
print(b <= 5)  # True

3.2.4 Logical Operators

Logical operators are used to combine multiple conditions.
Operator Description Example Output
and Returns True if both conditions are True (5 > 2) and (3 < 6) True
or Returns True if at least one condition is True (5 < 2) or (3 < 6) True
not Reverses the result (True → False, False → True) not(5 == 5) False 
a = 5
b = 10
c = 15

print(a < b and b < c)  # True (both conditions are True)
print(a > b or b < c)   # True (one condition is True)
print(not(a == 5))      # False (negates True)

3.2.5 Identity and Membership Operators

Identity Operators (is, is not)

  • Identity operators compare memory locations of objects (not just values).
Operator Description Example Output
is Returns True if both variables refer to the same object x is y True if same object
is not Returns True if variables refer to different objects x is not y True if different objects 
x = [1, 2, 3]
y = x  # y points to the same object as x
z = [1, 2, 3]  # z is a new object with same content

print(x is y)  # True (same memory reference)
print(x is z)  # False (different objects)
print(x is not z)  # True

Membership Operators (in, not in)

  • Membership operators check if a value exists in a sequence (like a list or string).
text = "Python programming"

print("Python" in text)  # True
print("java" in text)    # False
print("C++" not in text) # True
Key Takeaways.
✔ Strings are immutable sequences of characters.
✔ Triple quotes allow multi-line strings.
✔ Slicing and negative indexing help extract substrings.
✔ Concatenation joins strings using +.
✔ Python provides various string methods for manipulation.
✔ Python supports various operators for arithmetic, assignment, comparison, logical, identity, and membership operations.
✔ Arithmetic operators handle mathematical calculations.
✔ Assignment operators modify variables.
✔ Comparison operators return Boolean values.
✔ Logical operators evaluate multiple conditions.
✔ Identity operators check if two variables reference the same object.
✔ Membership operators verify if a value exists in a sequence.
 

Leave a Reply

Your email address will not be published. Required fields are marked *

sign up!

We’ll send you the hottest deals straight to your inbox so you’re always in on the best-kept software secrets.

© Copyright CODEMANIAC STUDIO ™

Twitter Facebook-square Linkedin Youtube
Operator Description Example Output
in Returns True if value exists in a sequence 'a' in 'apple' True
not in Returns True if value does not exist in a sequence 'z' not in 'apple' True