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Module 002: Your First Python Program

Phase: 1. Fundamentals | Estimated time: 1 hour | Milestone Project: No

Prerequisites

Learning Objectives

By the end of this module, you will be able to:

  • Use the print() function to display text
  • Write single-line and multi-line comments with #
  • Create string literals with single and double quotes
  • Pass multiple arguments to print()
  • Perform basic arithmetic inside print()
  • Create and run a .py file

Why This Matters

Every program you will ever write communicates something. The print() function is your first tool for making Python talk back to you. Mastering the basics of output and code organization sets the stage for everything that follows.

Concept Explanation

The print() Function

print() is a built-in Python function that displays output to the screen. You pass values inside the parentheses:

print("Hello, World!")
# Output: Hello, World!

The text inside quotes is called a string literal. You can use single quotes or double quotes — Python treats them the same:

print('Single quotes work too')
print("Double quotes work as well")

Multiple Arguments to print()

You can pass several items to print() separated by commas. They will be printed with a space between each:

print("Hello", "Python", "World!")
# Output: Hello Python World!

Simple Arithmetic in print()

You can put math expressions directly inside print(). Python evaluates the expression and prints the result:

print(2 + 3)
# Output: 5

print(10 - 4)
# Output: 6

print(3 * 7)
# Output: 21

print(8 / 2)
# Output: 4.0

Notice: division always produces a float (number with a decimal point).

Comments

Comments are notes for humans that Python ignores. Use the # symbol:

# This is a comment
print("Hello")  # This is also a comment after code

# You can have
# multi-line comments
# by starting each line with #

Use comments to explain why your code does something, not what it does (the code itself should show the what).

Running a .py File

Save your code in a file with the .py extension, then run it from the terminal:

python3 myprogram.py

Every line in the file executes in order, top to bottom.

Common Pitfalls

  1. Forgetting quotes: print(Hello) causes a NameError because Hello is not defined. Always quote strings.
  2. Mixing quote types inconsistently: Start and end with the same quote — print("hello') causes a SyntaxError.
  3. Missing parentheses: print "Hello" is Python 2 syntax. In Python 3, parentheses are required.
  4. Commas inside strings: print("Hello, World") is fine; commas between arguments are separators.
  5. Thinking print() returns a value: print() displays text but returns None.

Hands-On Walkthrough

Let's build a small program step by step.

  1. Create a file called greetings.py.
  2. Add a comment at the top: 
    # My first program - greetings
  3. Add a print statement with multiple arguments: 
    print("Welcome", "to", "Python", "3.12!")
  4. Add some arithmetic: 
    print("The answer to 2 + 3 is", 2 + 3)
  5. Add another print: 
    print("Goodbye!")
  6. Save the file and run it: 
    python3 greetings.py

Full file content:

# My first program - greetings
print("Welcome", "to", "Python", "3.12!")
print("The answer to 2 + 3 is", 2 + 3)
print("Goodbye!")

Expected output:

Welcome to Python 3.12!
The answer to 2 + 3 is 5
Goodbye!

Key Takeaways

  • print() displays output to the screen.
  • Strings must be enclosed in matching quotes (single or double).
  • Multiple arguments to print() are separated by commas and printed with spaces.
  • Arithmetic expressions inside print() are evaluated first, then printed.
  • Comments start with # and are ignored by Python.
  • Every .py file runs top to bottom.
  • Division (/) always returns a float.
  • Missing parentheses cause errors in Python 3.

Further Reading

Next Module

Learn how to store and work with data in Module 003: Variables and Data Types.