Variables in python

What is a Variable? A variable in Python is a container for storing data values. It acts as a container for data, allowing you to reference and manipulate it throughout your code.In other words it acts like a labeled box where you can store different types of information and retrieve them later. Example: Imagine a box labeled "favorite_color". If you put "blue" inside, that box now holds "blue". Declaring Variables A variable is created the moment you first assign a value to it. Python variables are dynamically typed, meaning you don’t need to specify their data type. The type is assigned automatically based on the value. name = "Vayola" age = 12 score = 95.5 What happens here? name holds the text "Vayola". age holds the number 12. score holds a decimal number 95.5. Variable Naming Rules Must start with a letter (a-z, A-Z) or an underscore (_). - Valid: `name`, `_age`, `Name1` - Invalid: `1name`, `@age` Cannot start with a number. - Valid: `age1` - Invalid: `1age` Can only contain alphanumeric characters and underscores (A-Z, a-z, 0-9,_). - Valid: `user_name`, `age_1` - Invalid: `user-name`, `age#1` Case-sensitive: myVar and myvar are different variables. Cannot be a reserved keyword (e.g., if, else, for, while, etc.). Examples of Variable Assignments # Integer x = 10 # Float y = 20.5 # String name = "Vayola" # Boolean is_valid = True # List my_list = [1, 2, 3, 4] # Tuple my_tuple = (1, 2, 3) # Dictionary my_dict = {"name": "Vayola", "age": 25} # Set my_set = {1, 2, 3} Variable Types Python supports various data types, and the type of a variable is determined by the value it holds. Common types include: Integer: x = 10 //Integer Float: y = 20.5 //Float String: name = "Vayola" //String Boolean: is_valid = True //Boolean List: my_list = [1, 2, 3] //List Tuple: my_tuple = (1, 2, 3) //Tuple Dictionary: my_dict = {"name": "Alice", "age": 25} //Dictionary Set: my_set = {1, 2, 3} //Set You can check the type of a variable using the type() function: x = 10 print(type(x)) # Output: Changing a Variable’s Value Variables are not permanent! You can change them anytime. color = "red" print(color) # Output: red color = "blue" print(color) # Output: blue First, color is "red". Then, we change it to "blue". Multiple Assignments Python allows you to assign values to multiple variables in a single line: a, b, c = 1, 2, 3 # a = 1, b = 2, c = 3 Can also assign like this too x = y = z = 10 # x, y, and z all have the value 10 Swapping Variables Python makes it easy to swap values between variables without needing a temporary variable x, y = 10, 20 x, y = y, x # Now x = 20 and y = 10 Deleting Variables You can delete a variable using the del keyword. Once deleted, the variable no longer exists in memory. x = 10 del x # x is deleted # print(x) # This will raise a NameError Combining Variables You can combine variables in Python! String Concatenation first_name = "Vayola" last_name = "Pradeep" full_name = first_name + " " + last_name # Combine with a space print(full_name) # Output: Vayola Pradeep Using f-strings name = "Vayola" age = 12 print(f"My name is {name} and I am {age} years old.") # Output: My name is Vayola and I am 12 years old. Variables in Math Operations Python allows you to perform calculations using variables. a = 10 b = 5 sum = a + b # Addition difference = a - b # Subtraction product = a b # Multiplication quotient = a / b # Division print(sum, difference, product, quotient) Special Variable: None None represents an empty or undefined value. result = None print(result) # Output: None result = 100 # Now it holds a value print(result) # Output: 100 Constants in Python A constant is a variable that should not change. Python doesn’t have built-in constants, but we use UPPERCASE names by convention. PI = 3.14159 GRAVITY = 9.8 Using Variables in a Simple Program Let’s create a program that asks for user input and prints a message. name = input("Enter your name: ") age = input("Enter your age: ") print(f"Hello {name}! You are {age} years old.") What Happens? input() takes user input. The input is stored in variables. The program prints a message using f-string. Scope of Variables The scope of a variable determines where it can be accessed in a program. There are two main types of variable scope in Python: Local Variables: Defined inside a function and accessible only within that function. Global Variables: Defined outside functions and accessible throughout the program. x = 10 # Global variable def my_function(): y = 20 # Local variable print(x) # Access global variable print(y) my_function() print(x) # Access global variable # print(y) # Th

Feb 12, 2025 - 05:24

What is a Variable?

A variable in Python is a container for storing data values. It acts as a container for data, allowing you to reference and manipulate it throughout your code.In other words it acts like a labeled box where you can store different types of information and retrieve them later.

Example:
Imagine a box labeled "favorite_color". If you put "blue" inside, that box now holds "blue".

Declaring Variables

A variable is created the moment you first assign a value to it. Python variables are dynamically typed, meaning you don’t need to specify their data type. The type is assigned automatically based on the value.

name = "Vayola"
age = 12
score = 95.5

What happens here?

name holds the text "Vayola".
age holds the number 12.
score holds a decimal number 95.5.

Variable Naming Rules

Must start with a letter (a-z, A-Z) or an underscore (_).

- Valid: `name`, `_age`, `Name1`

- Invalid: `1name`, `@age`

Cannot start with a number.

- Valid: `age1`

- Invalid: `1age`

Can only contain alphanumeric characters and underscores (A-Z, a-z, 0-9,_).

- Valid: `user_name`, `age_1`

- Invalid: `user-name`, `age#1`

Case-sensitive: myVar and myvar are different variables.

Cannot be a reserved keyword (e.g., if, else, for, while, etc.).

Examples of Variable Assignments

# Integer
x = 10

# Float
y = 20.5

# String
name = "Vayola"

# Boolean
is_valid = True

# List
my_list = [1, 2, 3, 4]

# Tuple
my_tuple = (1, 2, 3)

# Dictionary
my_dict = {"name": "Vayola", "age": 25}

# Set
my_set = {1, 2, 3}

Variable Types

Python supports various data types, and the type of a variable is determined by the value it holds. Common types include:

Integer: x = 10  //Integer
Float: y = 20.5 //Float
String: name = "Vayola" //String
Boolean: is_valid = True //Boolean
List: my_list = [1, 2, 3] //List
Tuple: my_tuple = (1, 2, 3) //Tuple
Dictionary: my_dict = {"name": "Alice", "age": 25} //Dictionary
Set: my_set = {1, 2, 3} //Set

You can check the type of a variable using the type() function:

x = 10
print(type(x))  # Output: <class 'int'>

Changing a Variable’s Value

Variables are not permanent! You can change them anytime.

color = "red"
print(color)  # Output: red

color = "blue"
print(color)  # Output: blue

First, color is "red". Then, we change it to "blue".

Multiple Assignments

Python allows you to assign values to multiple variables in a single line:

a, b, c = 1, 2, 3  # a = 1, b = 2, c = 3

Can also assign like this too

x = y = z = 10  # x, y, and z all have the value 10

Swapping Variables

Python makes it easy to swap values between variables without needing a temporary variable

x, y = 10, 20
x, y = y, x  # Now x = 20 and y = 10

Deleting Variables

You can delete a variable using the del keyword. Once deleted, the variable no longer exists in memory.

x = 10
del x  # x is deleted
# print(x)  # This will raise a NameError

Combining Variables

You can combine variables in Python!

String Concatenation

first_name = "Vayola"
last_name = "Pradeep"

full_name = first_name + " " + last_name  # Combine with a space
print(full_name)  # Output: Vayola Pradeep

*Using f-strings

name = "Vayola"
age = 12
print(f"My name is {name} and I am {age} years old.")  
# Output: My name is Vayola and I am 12 years old.

Variables in Math Operations

Python allows you to perform calculations using variables.

a = 10
b = 5

sum = a + b  # Addition
difference = a - b  # Subtraction
product = a * b  # Multiplication
quotient = a / b  # Division

print(sum, difference, product, quotient)

Special Variable: None

None represents an empty or undefined value.

result = None
print(result)  # Output: None

result = 100  # Now it holds a value
print(result)  # Output: 100

Constants in Python

A constant is a variable that should not change.
Python doesn’t have built-in constants, but we use UPPERCASE names by convention.

PI = 3.14159
GRAVITY = 9.8

Using Variables in a Simple Program

Let’s create a program that asks for user input and prints a message.

name = input("Enter your name: ")
age = input("Enter your age: ")

print(f"Hello {name}! You are {age} years old.")

What Happens?

input() takes user input.
The input is stored in variables.
The program prints a message using f-string.

Scope of Variables

The scope of a variable determines where it can be accessed in a program. There are two main types of variable scope in Python:

Local Variables: Defined inside a function and accessible only within that function.

Global Variables: Defined outside functions and accessible throughout the program.

x = 10  # Global variable

def my_function():
    y = 20  # Local variable
    print(x)  # Access global variable
    print(y)

my_function()
print(x)  # Access global variable
# print(y)  # This will raise an error because y is local to my_function```