Python Lesson 1: Your First Project – A Temperature Converter

Welcome! In this lesson we’ll write a simple Python program to convert temperatures (Fahrenheit to Celsius) while learning core concepts. Python is an interpreted, high-level, general-purpose programming language. This means you can write and run Python code line-by-line without a long compile step (interpreted), the code reads almost like English (high-level), and it’s used for everything from web apps to data science (general-purpose). Python’s syntax is designed for readability and simplicity, making it beginner-friendly. For example, the official Python site notes that “Python can be easy to pick up whether you’re a first time programmer or … experienced”. In other words, don’t worry if coding is new to you – Python was made to help people start programming gently.

Python can run on your computer or in an online notebook. We’ll use Google Colab (a free hosted Jupyter notebook) so you don’t even need to install anything. Colab is a cloud service that “requires no setup” and gives you a friendly environment to write and run Python code. It even provides free computing power. As you’ll see below, you can mix code cells (where you write Python) with text cells (for explanations) – and the interface shows line-by-line execution results in a console view.

Tools You’ll Use

  • Python 3: The latest version of Python. We’ll use features like the input() and print() functions.
  • Google Colab Notebook: An online editor you open in your web browser. No download needed; just sign in with your Google account.
  • Web Links for Reference: We’ll include links if you want to explore topics in depth, such as Python documentation or tutorials on data types and input/output.

Why Build a Temperature Converter?

Building a temperature converter is a fun first project. It has a clear goal (convert °F to °C) and uses simple math. In real life, you might use this if you’re a scientist recording weather data or a cook following a recipe from another country. By writing this converter, you’ll learn how to:

  • Get input from the user (e.g. asking “What’s the temperature in °F?”).
  • Store values in variables.
  • Perform a calculation (the conversion formula).
  • Display the output back to the user (showing the result in °C).

This project gives immediate results: you type a number, the program prints the converted temperature. It’s interactive and motivating for a beginner.

Understanding Variables

A variable in Python is like a labeled box that holds data. Imagine writing your name on a box and putting a number inside – you can later change the contents or label. In code, a variable has a name and stores a value (number, text, etc.). For example, we might use temp_f to hold the Fahrenheit temperature. In Python, you simply assign it like temp_f = 72. The act of assigning creates the box (variable) and labels it. Unlike some other languages, you don’t have to declare the type; Python figures out that 72 is a number.

👉 Quick check: What might happen if we later write temp_f = "72" (with quotes around 72)? (Answer: Python would treat it as text, and subtraction on it would cause an error.)

Think of variables as named containers. You can put a different value in temp_f later, and the old one is replaced. This is perfect for our converter because each time we run the program it can store a new input. (We’ll see an example soon.)

Figure: A computer screen showing a programming environment (code reflected in glasses). Python code looks like text, and we’ll type code similarly to run our temperature converter. In the above image, notice the open text editor with code. Python lets you write instructions (like boxes of data).

Getting Input and Output

To make our program interactive, we’ll use input() to ask the user for a number and print() to show the result. In Python, the input() function displays a prompt and returns what the user types as a string (text). For example:

user_input = input("Enter temperature in °F: ")

This line will pause the program and show the message. If the user types 100 and presses Enter, user_input will be "100" (a string!). You’ll often convert this to a number (with int() or float()) before doing math.

The print() function then shows values on the screen. It can print text and numbers together. For instance:

print("Converted to °C:", temp_c)

will display something like: Converted to °C: 37.78. In short, input and output let your program talk to the user. As one tutorial notes, “the input() function enables interaction with users by gathering input during program execution,” and print() displays the output.

Here’s an example of how it works in a session:

Enter temperature in °F: 100
The temperature in °C is: 37.78

(That output means the user typed 100 and the program printed the result.)

image1 Figure: A young programmer writing Python code on a computer. You’ll type code and see results on your screen as shown This image shows someone coding at a desk. You’ll do the same in Colab or any Python editor.

Planning with a Flowchart

Before coding, it often helps to sketch a flowchart of what the program will do. This is a simple diagram of steps:

image2Figure: Drawing a flowchart on a whiteboard, illustrating program logic as input ➔ process ➔ output.

  1. Input: Read the Fahrenheit temperature from the user.

  2. Process: Convert it to Celsius using the formula:

    \[\text{Celsius} = (\text{Fahrenheit} - 32) \times \tfrac{5}{9}.\]
  3. Output: Display the Celsius temperature.

This flowchart (above) shows boxes for each step. The left box is Input, the middle is Process, and the right is Output. Arrows show the flow: you start with the input value, apply the conversion, then show the result. Drawing this isn’t required, but it helps to think through the steps before writing code.

Writing the Code

Now let’s turn the plan into Python code. Open a new Colab notebook and add a code cell. We’ll write lines one by one, with comments and explanation:

# 1. Get user input for Fahrenheit temperature:
temp_f = float(input("Enter temperature in °F: "))

# 2. Convert to Celsius:
temp_c = (temp_f - 32) * 5/9

# 3. Output the result:
print("Temperature in °C is:", temp_c)
  • The first line uses input() to ask Enter temperature in °F:. We wrap input(...) inside float() to convert the entered text into a number (since input returns a string). Now temp_f is a numeric value we can do math with.
  • The second line applies the formula. We subtract 32, multiply by 5, then divide by 9. This follows the standard conversion.
  • The third line prints the result in a friendly message.

Run this cell. When prompted, type a number (like 100) and press Enter. You should see the program output something like:

Temperature in °C is: 37.77777777777778

That long decimal is okay, but we can format it later if needed. You’ve just written and executed your first Python program! 🎉

👉 Quick check: Try running the program with different inputs. What result do you expect if you enter 32? (Hint: 32°F should be 0°C.)

Common Errors (and How to Fix Them)

Every beginner makes mistakes – it’s totally normal! Let’s look at a few errors you might see, and how to fix them.

  • Type Error (String vs Number): If you forget float(), your code would be:

    temp_f = input("Enter temperature in °F: ")
temp_c = (temp_f - 32) * 5/9

    This causes an error because temp_f is a string and you can’t subtract 32 (an integer) from it. The program might crash with a message like:

    TypeError: unsupported operand type(s) for -: 'str' and 'int'

    To fix this, convert the input to a number (as shown above).

  • Syntax Error: Missing a parenthesis or colon can cause a SyntaxError. For example:

    print "Hello"

    (in Python 3, this needs parentheses: print("Hello")). Always check spelling and that parentheses match. The error message will point out something like “SyntaxError: invalid syntax” and underline the problem part.

  • Name Error: If you try to use a variable that doesn’t exist or is misspelled, Python says something like:

    NameError: name 'tempc' is not defined

    (Note: tempc vs temp_c are different names.) The fix is to double-check variable names for typos.

  • Indentation Error: Python uses spaces/tabs for structure. For this simple script we didn’t use extra blocks, but if you indent wrong (especially inside loops or if statements), you’ll get an IndentationError. The fix: align code correctly (each block should be indented the same amount).

Figure: A programmer frowning at code on his laptop, demonstrating common frustration from errors. Don’t worry – errors happen to everyone, and they help you learn!

Whenever you see an error, read the message carefully. It usually tells you what went wrong and where (it will show a line number). Use that clue to fix your code. If you’re stuck, ask a friend or look up the error – Google is very good at explaining error messages!

External Resources

Each of these links dives deeper into the topics we’ve touched on. Don’t worry if you don’t read them all now – they’re here for when you want to explore further.

Recap

  • Python is an interpreted, high-level language (easy to write and read). It’s beginner-friendly and widely used.
  • We used variables (temp_f, temp_c) to store values. Think of them as labeled boxes for data.
  • We gathered input with input() (remember it returns a string by default), and showed output with print().
  • Our temperature converter program took a Fahrenheit value, applied the conversion formula, and printed the Celsius result.
  • We sketched a flowchart to plan our steps: Input ➔ Process (convert) ➔ Output. Drawing it helped organize our thoughts.
  • We saw some common errors: string vs number mistakes, syntax typos, etc. These errors are normal – read the message and fix the code!

Great job on finishing your first Python lesson. You now have a working program and have learned key ideas about programming. 🎉

Mini-Challenge

Try to extend your temperature converter:

  • Modify the program so it asks for Celsius and converts to Fahrenheit. (Hint: formula is F = C * 9/5 + 32.)
  • Add extra output, e.g. after converting to °C, also print the value in Kelvin (K = C + 273.15).
  • Format the output to round to 2 decimal places: use Python’s round() function or f-strings (f”For example: {round(temp_c, 2)}”).

These mini-tasks reinforce what you’ve learned. Experiment and see what happens – that’s a big part of learning to code!

What’s Next?

  • Lesson 2 Preview: We’ll dive deeper into data types and more practice with variables. You’ll learn about integers vs. floats (whole numbers vs. decimals), and how to do simple math and string operations in Python.
  • Roadmap: Up next, we’ll cover conditional logic (making decisions with if), loops, and writing our own functions. Each lesson builds on the last, using projects to keep things exciting.

Keep up the great work! Remember, every programmer started with first steps like these. You’re on your way to creating even cooler projects. 🙌