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docs: Add Python YouTube Video tutorial (#7033)
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Adding the Python video tutorial to our docs for following along
<img width="887" alt="Screenshot 2024-05-10 at 7 06 21 AM"
src="https://github.com/Unleash/unleash/assets/22972707/69cdc8a3-b52f-49f7-857d-f907ada2744c">

https://youtu.be/-Rf0y2Gq8OA?si=udl3eIE9DdxQYGAY
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@nnennandukwe
nnennandukwe authored May 10, 2024
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71 changes: 26 additions & 45 deletions website/docs/feature-flag-tutorials/python/implementing-feature-flags.md
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@ title: How to Implement Feature Flags in Python
slug: /feature-flag-tutorials/python
---

import VideoContent from '@site/src/components/VideoContent.jsx';

[Python](https://www.python.org/) is a popular programming language used for a variety of software applications and services. It is supported widely in the developer community and is known for being intuitive, readable, and friendly to new and experienced developers.

Leveraging feature flags allows developers to toggle new features on and off, whether you’re experimenting in your local environment, testing for QA purposes, or rolling out changes to users in production. Feature flags play a critical role in optimizing the entire software development lifecycle. With Unleash, an open-source feature flag service, you can use our tooling to implement feature flags into your application and release new features faster, strategically, and safely. But how can you do this in Python?
Expand All @@ -16,6 +18,7 @@ In this tutorial, you will learn how to set up and use Python feature flags with
At the end of this tutorial, you will be able to turn on the feature flag and activate a route that will remove surveys from the database.

Here are the steps we will cover in this tutorial:

1. [Feature flag best practices for back-end applications](#1-unleash-best-practice-for-backend-apps)
2. [Spin up a local flag provider](#2-install-a-local-feature-flag-provider)
3. [Configure a feature flag](#3-create-and-configure-the-feature-flag)
Expand All @@ -24,16 +27,18 @@ Here are the steps we will cover in this tutorial:
6. [Verify the toggle experience](#6-verify-the-toggle-experience)
7. [Improve feature flag error handling](#7-improve-a-feature-flag-implementation-with-error-handling)

Watch the video tutorial and follow along with the code from this documentation.

## Prerequisites
<VideoContent videoUrls={["https://youtube.com/embed/-Rf0y2Gq8OA?si=udl3eIE9DdxQYGAY"]}/>

## Prerequisites

In this tutorial, you will need the following:
- A web browser like Chrome or Firefox
- Git
- Docker
- (Optional) a code editor like Visual Studio Code

- A web browser like Chrome or Firefox
- Git
- Docker
- (Optional) a code editor like Visual Studio Code

![An architectural diagram of our Python app using Unleash feature flags](/img/python-flask-unleash-architecture.png)

Expand All @@ -47,19 +52,17 @@ Since Python is a backend language, there are special security considerations to

Most importantly, you must:

- Limit feature flag payloads for scalability, security, and efficiency
- Improve architectural resiliency with graceful degradation
- Limit feature flag payloads for scalability, security, and efficiency
- Improve architectural resiliency with graceful degradation

As your application scales, performance and resiliency become more critical and costly if not addressed. A feature flagging system should not be the reason your app slows down or fails. That’s why we recommend you account for this by reducing the size of your feature flag payloads. For example, instead of making one large call to retrieve flag statuses for all users as part of your configuration, group your users by specific attributes as part of your targeting rules that would be most relevant for your application.

Additionally, our SDKs cache your feature flag configuration to help reduce network round trips and dependency on external services. You can rely on the cache if your Feature Flag Control Service is not available, which will mitigate potential failure in your application.

For a complete list of architectural guidelines, see our [best practices for building and scaling feature flag systems](https://docs.getunleash.io/topics/feature-flags/feature-flag-best-practices).


## 2. Install a local feature flag provider


There are many feature flag tools available. In this section, you will install Unleash, run the instance locally, log in, and create a feature flag, but you can use other tools in place of Unleash if you prefer. You’ll need to edit the code accordingly, but the basic steps will probably be the same.

Use Git to clone the Unleash repository and Docker to build and run it. Open a terminal window and run the following commands:
Expand All @@ -81,51 +84,40 @@ Password: unleash4all

Click the ‘New feature toggle’ button to create a new feature flag. Once you have created a flag, you will see it here.


![Image of the Unleash platform to create a new feature flag](/img/tutorial-create-flag.png)


## 3. Create and configure the feature flag


Next, you will create a feature flag and turn it on for your Python app.

In the Create Toggle view, give your feature flag a unique name and click ‘Create toggle feature’.

For the purpose of this tutorial, name the feature flag `delete_survey_flag`. Use the default values in the rest of the feature flag form.


![Image of a feature flag form](/img/python-tutorial-feature-flag-form.png)


Your new feature flag has been created and is ready to be used. Enable the flag for your development environment, which makes it accessible for use in the Python app we will clone into your local environment.


![Image of the enabled Python flag in development environment](/img/python-tutorial-enabled-flag.png)

Next, generate an API token to authenticate calls made to Unleash servers from your project. This API token will eventually be pulled into a configuration object within your Python application to toggle features.
Next, generate an API token to authenticate calls made to Unleash servers from your project. This API token will eventually be pulled into a configuration object within your Python application to toggle features.

> **Note** We require an API token as part of your flag configuration to ensure that only applications with the correct authentication can access your feature flags in Unleash. API tokens are created by users with API management access and thus controls how they can be distributed to applications that need it, and by whom.
From your project view on the platform, go to "Project Settings" and then "API Access".

Select the ‘New API token’ button.


![Image of the API token button in API Access view](/img/tutorial-create-api-token.png)


Name the API token and select the “Server-side SDK” token type, since we’ll be doing our flag evaluation on the server using the Python SDK. You can read more about [Unleash API tokens in our documentation](https://docs.getunleash.io/reference/api-tokens-and-client-keys#client-tokens).

The token should have access to the “development” environment, as shown in the platform screenshot below.


![Image of the API token creation form](/img/tutorial-create-api-token.png)


The API token you generated can be managed in the API Access view in your project settings. It will become handy in Step 4.


## 4. Add Unleash to a Python app

In this section, you will clone an open-source Python application called [Flask Surveys Container app](https://github.com/pamelafox/flask-surveys-container-app), which we are using to model a service that provides routing, serves HTML pages, and performs actions against a database. This app uses Flask, SQLAlchemy, and a PostgreSQL database.
Expand All @@ -140,7 +132,6 @@ Next, navigate into your repository directory and create a `.env` file.

Copy this code snippet into your `.env` file:


```py
FLASK_DEBUG=True
DBHOST=db
Expand All @@ -149,33 +140,27 @@ DBUSER=app_user
DBPASS=app_password
```


Next, install the Python SDK. Open your repository in a code editor and navigate to `requirements.txt` inside the `src` folder. Reference the Python SDK for installation.


```py
UnleashClient==5.11.1
```


In `src/backend/__init__.py`, import `UnleashClient`:


```py
from UnleashClient import UnleashClient
```


In the same file, call the Unleash client for initialization when the app runs with this code snippet:


```py
client = UnleashClient(
url="http://host.docker.internal:4242/api",
app_name="flask-surveys-container-app",
custom_headers={'Authorization': '<API token>'}
)

client.initialize_client()
```

Expand All @@ -187,18 +172,14 @@ You can check our [API token and client keys documentation](https://docs.getunle

Next, go to your terminal and build the app using this command:


```
docker-compose up --build
```


Navigate to [localhost://50505](http://localhost://50505) and the Surveys list should eventually display:


![Image of Surveys app loaded in browser](/img/python-tutorial-surveys-app-loaded.png)


Create 1 or more new surveys so they’re populated in your database!

## 5. Use a feature flag to release a delete method
Expand All @@ -208,10 +189,11 @@ In a real-world use case for your feature flag, you can roll out new features to
In this case, our app currently supports creating a survey, but once we create one, we can’t get rid of it. We want to roll out a ‘delete’ button in our list of surveys to all users so we have the option to remove them from our database.

This will require us to:
- Create a new route in our app
- Create a method that deletes a survey based on survey ID
- Create a delete button
- Map the delete button to the delete method

- Create a new route in our app
- Create a method that deletes a survey based on survey ID
- Create a delete button
- Map the delete button to the delete method

First, we need an error handler to return a simple 404 page to stop a user from being able to delete a survey when the flag is off. We will use this function in our delete method.

Expand All @@ -225,7 +207,6 @@ from flask import redirect, render_template, request, url_for, abort

Add `client` to the `backend` import statement on line 4. The full import line will now look like this:


```py
from backend import db, client
```
Expand Down Expand Up @@ -265,24 +246,26 @@ In `src/backend/templates/surveys_list.html`, add the following code to your sur

```html
{% if client.is_enabled('delete_survey_flag') %}
<td class="text-end"><a href="{{ url_for('surveys.delete_survey', survey_id=survey.id) }}" class="btn btn-sm btn-danger">Delete</a></td>
<td class="text-end">
<a
href="{{ url_for('surveys.delete_survey', survey_id=survey.id) }}"
class="btn btn-sm btn-danger"
>Delete</a
>
</td>
{% endif %}
```

This code wraps a delete button in a conditional statement that checks whether or not the feature flag is enabled. This button has a link that points to the `delete_survey` method we created, which will pull in the survey using an ID to search the database, find the matching survey, and delete it from the session.

Your surveys page will now look something like this:


![Screenshot of app in browser with delete buttons in survey table](/img/python-tutorial-surveys-with-delete.png)


Test the new functionality by deleting one of your surveys. The page should refresh without the survey you deleted.


## 6. Verify the toggle experience


Now that we’ve added in new functionality and connected it to our feature flag, we can verify that if you disable the flag in your development environment, your Python app will no longer serve an HTML page with the option to delete surveys you’ve created.

In your local Unleash instance, turn off the feature flag by disabling it in the development environment.
Expand All @@ -295,10 +278,8 @@ Next, return to your Survey app and refresh the browser. With the flag disabled,
![Screenshot of app in browser without delete buttons for surveys](/img/python-tutorial-surveys-without-delete.png)


## Conclusion


In this tutorial, we ran Unleash locally, created a new feature flag, installed the Python SDK into a Python Flask app, and toggled new functionality that altered a database with a containerized project!

Continue to our [Python Examples docs](/feature-flag-tutorials/python/examples) for more advanced applications of feature flags in Python using our Flask Surveys Containers App!

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