Python Variables, Data Types, Operators, Functions, and Control Flow

Variables in Python

In Python, a variable holds a value and is assigned with a name for reference. Names follow certain rules such as starting with a letter or underscore, containing alphanumeric characters plus underscores, and being case-sensitive. Assign values to variables using variable_name = value. To change the value later, simply assign a different value to the existing variable. Variables come in various forms depending on the type of data stored—integers, floats, strings, boolean, lists, and tuples are among the most commonly encountered.

Here is an example of declaring and changing the value of a variable called age storing a whole number.

## Declare the variable age
age = 42

print("Current age:", age)

## Change the age to 45
age = 45

print("\nNew age:", age)

Output: Current age: 42 New age: 45

Data Types in Python

Data types determine how data is interpreted and manipulated. Common data types include integers, floating point numbers, strings, booleans, and objects for structured data like lists and tuples. Each data type has its associated operations.

For instance, integer arithmetic supports addition (+), subtraction (-), multiplication (*), division (/) and floor division (%), whereas string components can be accessed via indexing.

Operators in Python

Operators perform mathematical or logical actions on operands, resulting in a value. Arithmetic operators like +, -, *, / handle basic calculations. Comparison operators like >, <, ==, != compare values and evaluate to True or False according to the result. Logical operators and, or, not combine conditions with Boolean logic. Bitwise operators perform bit-by-bit operations on integers.

Consider the expression:

a = 4
b = 2
result = a + b

print(result)

Output: 6

Here, the + operator adds the values of a and b.

Functions in Python

Functions define blocks of code that can be repeatedly used, accepting parameters and returning a value. They help modularize application design.

Define a factorial function, factorial(num), that returns the factorial of a non-negative integer number num. Factorials calculate the product of all positive integers less than or equal to num.

def factorial(num):
    '''Calculate factorial'''
    if num == 0:
        return 1
    elif num > 0:
        return num * factorial(num-1)

## Example usage
print("Factorial of 5 is:", factorial(5))

Output: Factorial of 5 is: 120

Control Flow in Python

Control flow manages the execution order of statements within loops or conditionals. Loops iterate until a termination criterion is met, while conditional statements select paths based on truth-values.

Below is a simple loop printing odd numbers between 1 and 10 using a while statement.

i = 1
while i <= 10:
    print(i)
    i += 2

Output: 1 3 5 7 9