Variables

What is a variable?

In programming a variable is often referred to as named storage location that stores a data or value. The data or value stored in a variable may change through out the program execution.

Variables data type

A variable data type is a refers to the type of value or data a variable is storing.

Variables data type in python are derived from the value they store, because Python is a dynamically-typed, meaning the variable data type is subject to change with respect to change of its value type.

Constants

A constant is a value or data which can be used but can’t be modified during the program execution. It stores a fixed value unlike a variable whose value can be changed.

It’s value is meant to not be modified once assigned.

Defining a constant

When defining a constant, all the characters of the constant name should be in upper case.

  PI =  3.14
  MONTHS = 12

Variable - Naming conventions:

Variable naming conventions are a set of guidelines that helps in choosing a descriptive and meaningful names for variables. Which helps make the code more readable and maintainable if consistently adhered to.

• variable name should be descriptive and meaningful

• Do not use abriviations unless widely used (e.g., URL)

• Use lowercase letters, underscores, and numbers (e.g., my_variable)

• Avoid using special characters like $ and _ as the first character

• if a variable name contains more than one word then join them using use underscore _ (e.g., my_seond_variable)

• Constants are written in all uppercase (e.g., PI)

Example

  # acceptable variable name
  department = "Computer Science"

  # not acceptable SyntaxError: invalid decimal literal
  3department = " "

Things to know:

1. A variable maybe referenced by several different identifiers.

2. Assigning a value to a variable using one of identifiers will change the value that can be accessed through other identifiers.

Scope of a variable

Scope of variable determines its accessibility within a program, in simple terms, it determines from where within your code you can use a variable.

Global-variable

Global variables have a global scope therefore they are accessible everywhere within your code.

global variable

# Global variable
name = "Alice"

def greet():
    # Accessing the global variable inside the function
    print("Hello, " + name + "!")

def change_name(new_name):
    global name  # Declaring that we want to modify the global variable
    name = new_name

# Call the functions
greet()  # Output: Hello, Alice!

change_name("Bob")
greet()  # Output: Hello, Bob!

Local-variable

Local variables have a local scope therefore they are only accessible within a function or block scope.

local variable

def greet():
    # Local variable
    name = "Alice"
    print("Hello, " + name + "!")

def change_name():
    # This 'name' variable is local to this function and different from the one in greet()
    name = "Bob"
    print("Inside change_name, name is: " + name)

# Call the functions
greet()           # Output: Hello, Alice!
change_name()     # Output: Inside change_name, name is: Bob

# Trying to access the local variable outside the function will cause an error
# print(name)     # Uncommenting this line will result in a NameError