### <a href="https://flask.palletsprojects.com" class="external-link" target="_blank">Flask</a>

Flask is a "microframework", it doesn't include database integrations nor many of the things that come by default in Django.

This simplicity and flexibility allow doing things like using NoSQL databases as the main data storage system.

As it is very simple, it's relatively intuitive to learn, although the documentation gets somewhat technical at some points.

* A particular program while it is **running** on the operating system.
    * This doesn't refer to the file, nor to the code, it refers **specifically** to the thing that is being **executed** and managed by the operating system.

If you generate a client for a FastAPI app using tags, it will normally also separate the client code based on the tags.

This way you will be able to have things ordered and grouped correctly for the client code:

<img src="/img/tutorial/generate-clients/image06.png">

In this case you have:

* `ItemsService`
* `UsersService`

### Client Method Names

    {!> ../../../docs_src/response_model/tutorial003_01.py!}
    ```

With this, we get tooling support, from editors and mypy as this code is correct in terms of types, but we also get the data filtering from FastAPI.

How does this work? Let's check that out. 🤓

### Type Annotations and Tooling

First let's see how editors, mypy and other tools would see this.

So, to avoid ID collisions, when creating the JWT token for the user, you could prefix the value of the `sub` key, e.g. with `username:`. So, in this example, the value of `sub` could have been: `username:johndoe`.

The important thing to keep in mind is that the `sub` key should have a unique identifier across the entire application, and it should be a string.

## Check it

**"Dependency Injection"** means, in programming, that there is a way for your code (in this case, your *path operation functions*) to declare things that it requires to work and use: "dependencies".

And then, that system (in this case **FastAPI**) will take care of doing whatever is needed to provide your code with those needed dependencies ("inject" the dependencies).

This is very useful when you need to:

### Tests

* Help me check that the PR has **tests**.

* Check that the tests **fail** before the PR. 🚨

* Then check that the tests **pass** after the PR. ✅

* Many PRs don't have tests, you can **remind** them to add tests, or you can even **suggest** some tests yourself. That's one of the things that consume most time and you can help a lot with that.

⚫️ 🌅 🌟 🐍 🛠️ & 🛎 🕴. ⚫️ ⚙️ 🏗 ⚙️ 💖 👱📔.

⚫️ 📶 😆 🔗 ⏮️ 🔗 💽 (💖 ✳ ⚖️ ✳),, ✔️ ☁ 💽 (💖 🗄, ✳, 👸, ♒️) 👑 🏪 🚒 🚫 📶 ⏩.

⚫️ ✍ 🏗 🕸 👩‍💻, 🚫 ✍ 🔗 ⚙️ 🏛 🕸 (💖 😥, Vue.js &amp; 📐) ⚖️ 🎏 ⚙️ (💖 <abbr title="Internet of Things">☁</abbr> 📳) 🔗 ⏮️ ⚫️.

### <a href="https://www.django-rest-framework.org/" class="external-link" target="_blank">✳ 🎂 🛠️</a>

✳ 🎂 🛠️ ✍ 🗜 🧰 🏗 🕸 🔗 ⚙️ ✳ 🔘, 📉 🚮 🛠️ 🛠️.

⚫️ ⚙️ 📚 🏢 ✅ 🦎, 🟥 👒 &amp; 🎟.

You would probably do this just once, the first time, when setting everything up.

!!! tip
    This Domain Name part is way before HTTPS, but as everything depends on the domain and the IP address, it's worth mentioning it here.

### DNS

Now let's focus on all the actual HTTPS parts.

First, the browser would check with the **DNS servers** what is the **IP for the domain**, in this case, `someapp.example.com`.

Python has support for optional "type hints" (also called "type annotations").

These **"type hints"** or annotations are a special syntax that allow declaring the <abbr title="for example: str, int, float, bool">type</abbr> of a variable.

By declaring types for your variables, editors and tools can give you better support.