Introduction to Python 101

Introduction to Python 101

The Ultimate Python Crash Course

Lesson 1: Introduction to Python

Welcome to the Introduction to Python course! In this lesson, we will cover the basics of Python programming language.

Installing Python

To get started, you need to install Python on your computer. You can download the latest version of Python from the official website ( Follow the installation instructions for your operating system to complete the installation.

Python Interpreter

Python code can be executed in two ways: in a script file or using the Python interpreter. The Python interpreter is an interactive shell that allows you to execute Python code on the fly. To start the Python interpreter, open a terminal window and type "python" without quotes. You should see the Python prompt ">>>".

Basic Syntax

Python code is written in a straightforward syntax that is easy to read and write. Here is an example of a Python program that prints "Hello, World!" to the console:

print("Hello, World!")

Variables and Data Types

Variables are used to store data in Python. In Python, you don't need to specify the data type of a variable - Python infers the type based on the value assigned to it. Here is an example of a Python program that uses variables:

name = "John"
age = 30
height = 1.75

In this example, we have three variables: name, age, and height. The first variable is a string, the second is an integer, and the third is a float.

Control Structures

Python has several control structures that allow you to control the flow of your program. The most common control structures in Python are if/else statements and loops.

Here is an example of an if/else statement:

x = 5
if x > 10:
    print("x is greater than 10")
    print("x is less than or equal to 10")

Here is an example of a loop:

for i in range(0, 5):


Functions are used to encapsulate a block of code that can be reused throughout your program. Here is an example of a Python function:

def square(x):
    return x * x

In this example, we have defined a function called "square" that takes one argument, "x". The function returns the square of the argument.

File Input/Output

Python provides built-in functions for reading from and writing to files. Here is an example of a Python program that reads from a file and prints the contents to the console:

with open("file.txt", "r") as f:
    for line in f:

In this example, we have opened the file "file.txt" in read mode and printed each line to the console.


In this lesson, we have covered the basics of Python programming language. You should now have a solid understanding of the Python syntax, variables and data types, control structures, functions, and file input/output. In the next lesson, we will explore more advanced Python topics.

Coding Challenge

Write a Python program that takes a list of numbers as input and returns the sum of all the even numbers in the list.

Here's an example of what the program should do:

Input: [1, 2, 3, 4, 5, 6]
Output: 12

In this example, the even numbers in the list are 2, 4, and 6, and their sum is 12.

To solve this challenge, you can use a loop to iterate over the list and an if statement to check if each number is even. If a number is even, add it to a running total of even numbers. At the end of the loop, return the total.

Here's some starter code to help you get started:

def sum_even_numbers(numbers):
    total = 0
    for num in numbers:
        if num % 2 == 0:
            # add num to total
    return total

Your task is to complete the sum_even_numbers function by filling in the missing code. Good luck!

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Happy Coding!