Introduction

Reflex is an open-source framework for quickly building beautiful, interactive web applications in pure Python.

Goals

Pure Python

Use Python for everything. Don't worry about learning a new language.

Easy to Learn

Build and share your first app in minutes. No web development experience required.

Full Flexibility

Remain as flexible as traditional web frameworks. Reflex is easy to use, yet allows for advanced use cases.

Build anything from small data science apps to large, multi-page websites. This entire site was built and deployed with Reflex!

Batteries Included

No need to reach for a bunch of different tools. Reflex handles the user interface, server-side logic, and deployment of your app.

An example: Make it count

Here, we go over a simple counter app that lets the user count up or down.

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Here is the full code for this example:

The frontend is built declaratively using Reflex components. Components are compiled down to JS and served to the users browser, therefore:

Only use Reflex components, vars, and var operations when building your UI. Any other logic should be put in your State (backend).
Use rx.cond and rx.foreach (replaces if statements and for loops), for creating dynamic UIs.

The Structure of a Reflex App

Let's break this example down.

Import

We begin by importing the reflex package (aliased to rx). We reference Reflex objects as rx.* by convention.

State

The state defines all the variables (called vars) in an app that can change, as well as the functions (called event_handlers) that change them.

Here our state has a single var, count, which holds the current value of the counter. We initialize it to 0.

Event Handlers

Within the state, we define functions, called event handlers, that change the state vars.

Event handlers are the only way that we can modify the state in Reflex. They can be called in response to user actions, such as clicking a button or typing in a text box. These actions are called events.

Our counter app has two event handlers, increment and decrement.

User Interface (UI)

This function defines the app's user interface.

We use different components such as rx.hstack, rx.button, and rx.heading to build the frontend. Components can be nested to create complex layouts, and can be styled using the full power of CSS.

Reflex comes with 50+ built-in components to help you get started. We are actively adding more components. Also, it's easy to wrap your own React components.

Components can reference the app's state vars. The rx.heading component displays the current value of the counter by referencing State.count. All components that reference state will reactively update whenever the state changes.

Components interact with the state by binding events triggers to event handlers. For example, on_click is an event that is triggered when a user clicks a component.

The first button in our app binds its on_click event to the State.decrement event handler. Similarly the second button binds on_click to State.increment.

In other words, the sequence goes like this:

User clicks "increment" on the UI.
on_click event is triggered.
Event handler State.increment is called.
State.count is incremented.
UI updates to reflect the new value of State.count.

Add pages

Next we define our app and add the counter component to the base route.

Next Steps

🎉 And that's it!

We've created a simple, yet fully interactive web app in pure Python.

By continuing with our documentation, you will learn how to building awesome apps with Reflex.

For a glimpse of the possibilities, check out these resources:

For a more real-world example, check out either the dashboard tutorial or the chatapp tutorial.
We have bots that can answer questions and generate Reflex code for you. Check them out in #ask-ai in our Discord!