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Python Variables

Hello Friends. In my last post, we discussed about String manipulation using built-in functions. In this post I will talk about the concept of python variables.

Variables are used to store data values. They are like containers that hold information which can be referenced and manipulated throughout the program. Variables in Python are dynamically typed, meaning you don’t need to explicitly declare the type of a variable before assigning a value to it.

Here’s an explanation with examples:

message = "Hello Proedu!"
marks = 100
print(message)
print(marks)

# Output
# Hello Proedu!
# 100

In this example, variable message is assigned the String value Hello Proedu!, and variable marks is assigned the integer value 100.

Variable naming rules in Python

Variable name should be descriptive enough to show the actual purpose of variable but you can also create variables with names like x and y. Below are python rules for naming a variable:

• Variable ame must start with a letter or the underscore character but it cannot start with a number.
• Variable name can only contain alpha-numeric characters and underscores i.e (A-z, 0-9, and _ ).
• Variable names are case-sensitive (proedu, Proedu and PROEDU are three different variables).
• Variable name must not be any of the Python keywords.

Here are some examples of legal variables names:

proedu = "Proedu Examples"
pro_edu = "Proedu Examples"
_pro_edu = "Proedu Examples"
proEdu = "Proedu Examples"
Proedu = "Proedu Examples"
PROEDU = "Proedu Examples"
proedu1 = "Proedu Examples"
print(proedu)
print(pro_edu)
print(_pro_edu)
print(proEdu)
print(Proedu)
print(PROEDU)
print(proedu1)

# Output
# Proedu Examples
# Proedu Examples
# Proedu Examples
# Proedu Examples
# Proedu Examples
# Proedu Examples
# Proedu Examples

Here are some examples of Illigal variables names:

2proedu = "Proedu Examples"
print(2proedu)
# SyntaxError: invalid decimal literal

pro-edu = "Proedu Examples"
print(pro-edu)
# SyntaxError: cannot assign to expression here.

pro edu = "Proedu Examples"
print(pro edu)
# SyntaxError: invalid syntax

Variable reassignment in python

Python allows you to re-assign a different value to a variable, even if it is having a different data type. Here is an example

# Creating a variable.
message = "Hello Proedu!"
print(message)

# Re-assigning a new value of same data type.
message = "Hi Again"
print(message)

# Re-assigning a new value of different data type.
message = 100
print(message)

# Output
# Hello Proedu!
# Hi Again
# 100

Multiple Assignment

Python allows you to assign values to multiple variables in one line. Here is an example

length, width, height = 10, 8, 6
print("Volume of Cuboid: "+str(length * width * height))

# Output
# Volume of Cuboid: 480

We can also assign the same value to multiple variables as shown below

length = width = height = 10
print("Volume of Cuboid: "+str(length * width * height))

# Output
# Volume of Cuboid: 1000

Unpacking a collection to multiple variables

Unpacking extracts values of a collection to multiple variables as shown below

days_of_week = [10, 8 , 6]
length, width, height = days_of_week
print(length)
print(width)
print(height)

# Output
# 10
# 8
# 6

Global variables and Local variables in python

Global variables are accessible throughout the program, while local variables are accessible only within the defined function. Here is an example

# Creating a Global variable.
global_var = 100

def my_function():
    # Local variable
    local_var = 50
    print("Inside the function:", local_var)

my_function()
print("Outside the function:", global_var)

# Output
# Inside the function: 50
# Outside the function: 100

In this example, global_var is a global variable accessible throughout the program, while local_var is a local variable accessible only within the my_function() function. If we try to access local_var outside the function, it will result into an error.

# Creating a Global variable.
global_var = 100

def my_function():
    # Local variable
    local_var = 50
    print("Inside the function:", local_var)

my_function()
print("Outside the function:", global_var)
print("Accessing local variable outside function: ", local_var)

# Output
# NameError: name 'local_var' is not defined. Did you mean: 'global_var'?

Can we create a global variable inside a function – global keyword

To create a global variable inside a function, you can use the global keyword.

global_var = 100
def my_func():
    global global_inside_func
    global_inside_func = 200

print("Global Variable:", global_var)
my_func()
print("Global variable defined inside function", global_inside_func)

# Output
# Global Variable: 100
# Global variable defined inside function 200

In this example, we have created a global variable named global_inside_func inside function my_func. This variable can be accessed outside the scope of the function as well.

Modifying a global variable inside a function

To change the value of a global variable inside a function, refer to the variable by using the global keyword as shown below

message = "Hello Proedu!!!"
def my_func():
    global message
    message = "Hi Again!!!"

print("Original Message: ", message)
my_func()
print("Modified Message: ", message)

# Output
# Original Message:  Hello Proedu!!!
# Modified Message:  Hi Again!!!Output