# Reference - Code API

Here's the reference or code API, the classes, functions, parameters, attributes, and
all the FastAPI parts you can use in your applications.

If you want to **learn FastAPI** you are much better off reading the

## Dependencies for groups of *path operations*

And you want to have a way for the frontend to authenticate with the backend, using a **username** and **password**.

We can use **OAuth2** to build that with **FastAPI**.

But let's save you the time of reading the full long specification just to find those little pieces of information you need.

Let's use the tools provided by **FastAPI** to handle security.

## How it looks

## 🔑 👨‍💼

### ⚫️❔ "🔑 👨‍💼"

"🔑 👨‍💼" 🙆 👈 🐍 🎚 👈 👆 💪 ⚙️ `with` 📄.

🖼, <a href="https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files" class="external-link" target="_blank">👆 💪 ⚙️ `with` ✍ 📁</a>:

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

## Recap

You have been reading here some of the main concepts that you would probably need to keep in mind when deciding how to deploy your application:

* Security - HTTPS
* Running on startup
* Restarts

    * PR [#593](https://github.com/tiangolo/fastapi/pull/593).
* Improve handling of custom classes for `Request`s and `APIRoute`s.
    * This helps to more easily solve use cases like:
        * Reading a body before and/or after a request (equivalent to a middleware).
        * Run middleware-like code only for a subset of *path operations*.

That's why in this example we have to declare it in the `response_model` parameter.

...but continue reading below to see how to overcome that.

## Return Type and Data Filtering

Let's continue from the previous example. We wanted to **annotate the function with one type** but return something that includes **more data**.

### <a href="https://webargs.readthedocs.io/en/latest/" class="external-link" target="_blank">Webargs</a>

Another big feature required by APIs is <abbr title="reading and converting to Python data">parsing</abbr> data from incoming requests.

Webargs is a tool that was made to provide that on top of several frameworks, including Flask.

!!! check "😮 **FastAPI** "
    ⚙️ 📟 🔬 "🔗" 👈 🚚 💽 🆎 & 🔬, 🔁.

### <a href="https://webargs.readthedocs.io/en/latest/" class="external-link" target="_blank">Webarg</a>

➕1️⃣ 🦏 ⚒ ✔ 🔗 <abbr title="reading and converting to Python data">✍</abbr> 📊 ⚪️➡️ 📨 📨.

Webarg 🧰 👈 ⚒ 🚚 👈 🔛 🔝 📚 🛠️, 🔌 🏺.

⚫️ ⚙️ 🍭 🔘 💽 🔬. &amp; ⚫️ ✍ 🎏 👩‍💻.

⚫️ 👑 🧰 &amp; 👤 ✔️ ⚙️ ⚫️ 📚 💁‍♂️, ⏭ ✔️ **FastAPI**.

!!! info

### Create Pydantic *models* / schemas for reading / returning

Now create Pydantic *models* (schemas) that will be used when reading data, when returning it from the API.

For example, before creating an item, we don't know what will be the ID assigned to it, but when reading it (when returning it from the API) we will already know its ID.