Real Python: Model-View-Controller (MVC) in Python Web Apps: Explained With Lego

If you’re curious about web development, then you’ve likely encountered the abbreviation MVC, which stands for Model-View-Controller. You may know that it’s a common design pattern that’s fundamental to many Python web frameworks and even desktop applications.

But what exactly does it mean? If you’ve had a hard time wrapping your head around the concept, then keep on reading.

In this tutorial, you’ll:

• Approach understanding the MVC pattern through a Lego-based analogy
• Learn what models, views, and controllers are conceptually
• Tie your conceptual understanding back to concrete web development examples
• Investigate Flask code snippets to drive the point home

Maybe you built things with Lego as a kid, or maybe you’re still a Lego-aficionado today. But even if you’ve never pieced two Lego blocks together, keep on reading because the analogy might still be a good building block for your understanding.

Explaining the Model-View-Controller Pattern With Lego

Imagine that you’re ten years old and sitting on your family room floor. In front of you is a big bucket of Lego, or similar modular building blocks. There are blocks of all different shapes and sizes:

• 🟦🟦🟦 Some are blue, tall, and long.
• 🟥 Some are red and cube-shaped.
• 🟨🟨 Some are yellow, big, and wide.

With all of these different Lego pieces, there’s no telling what you could build!

Just as your mind is filling with the endless possibilities, you hear something coming from the direction of the couch. It’s your older brother, voicing a specific request. He’s saying, “Hey! Build me a spaceship!”

“Alright,” you think, “that could actually be pretty cool.” A spaceship it is!

So you get to work. You start pulling out the Lego blocks that you think you’re going to need. Some big, some small. Different colors for the outside of the spaceship, different colors for the engines.

Now that you have all of your building blocks in place, it’s time to assemble the spaceship. And after a few hours of hard work, you now have in front of you—a spaceship:

                                  🟦
                                🟦🟥🟦
                              🟦🟥🟥🟥🟦
                            🟦🟥🟥🟥🟥🟥🟦
                            🟦🟥🟥🟥🟥🟥🟦
                            🟦🟥🟩🟩🟩🟥🟦
                            🟦🟥🟩🟦🟩🟥🟦
                            🟦🟥🟩🟩🟩🟥🟦
                            🟦🟥🟥🟥🟥🟥🟦
                            🟦🟥🟥🟥🟥🟥🟦
                            🟦🟥🟥🟥🟥🟥🟦
                        🟦🟥🟥🟥🟥🟥🟥🟥🟥🟥🟦
                        🟦🟥🟥🟥🟥🟥🟥🟥🟥🟥🟦
                        🟦🟥🟨🟨🟥🟥🟥🟨🟨🟥🟦
                            🟨🟨       🟨🟨

You run to find your brother and show him the finished product. “Wow, nice work!”, he says. Then he quietly adds:

Huh, I just asked for that a few hours ago, I didn’t have to do a thing, and here it is. I wish everything was that easy.

— Your Brother

What if I told you that building a web application using the MVC pattern is exactly like building something with Lego blocks?

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