The **Advanced User Guide** builds on this one, uses the same concepts, and teaches you some extra features.

But you should first read the **Tutorial - User Guide** (what you are reading right now).

**projects depend on**. That's very difficult to manage. And you would probably end up running some projects with some **incompatible versions** of the packages, and not knowing why something isn't working.

Also, depending on your operating system (e.g. Linux, Windows, macOS), it could have come with Python already installed. And in that case it probably had some packages pre-installed with some specific versions **needed by your system**. If you install packages in the global Python environment,...

        ClassPath.getClassPathEntry(new File("/home/build/outer.jar"), "file:/usr/test/dep.jar")
            .toURI());
    assertEquals(
        new File("/home/build/a.jar").toURI(),
        ClassPath.getClassPathEntry(new File("/home/build/outer.jar"), "a.jar").toURI());
    assertEquals(
        new File("/home/build/x/y/z").toURI(),
        ClassPath.getClassPathEntry(new File("/home/build/outer.jar"), "x/y/z").toURI());

        return this.profilePath;
    }

    /**
     * Returns the user's home directory path.
     * @return the home directory path
     */
    public String getHomeDirectory() {
        return this.homeDirectory;
    }

    /**
     * Returns the user's home drive letter.
     * @return the home drive
     */
    public String getHomeDrive() {
        return this.homeDrive;
    }

# History, Design and Future { #history-design-and-future }

Some time ago, <a href="https://github.com/fastapi/fastapi/issues/3#issuecomment-454956920" class="external-link" target="_blank">a **FastAPI** user asked</a>:

> What’s the history of this project? It seems to have come from nowhere to awesome in a few weeks [...]

Here's a little bit of that history.

## Alternatives { #alternatives }

**FastAPI** provides several tools to help you deal with **Security** easily, rapidly, in a standard way, without having to study and learn all the security specifications.

But first, let's check some small concepts.

## In a hurry? { #in-a-hurry }

If you don't care about any of these terms and you just need to add security with authentication based on username and password *right now*, skip to the next chapters.

### `HTMLResponse` { #htmlresponse }

Takes some text or bytes and returns an HTML response, as you read above.

### `PlainTextResponse` { #plaintextresponse }

Takes some text or bytes and returns a plain text response.

{* ../../docs_src/custom_response/tutorial005.py hl[2,7,9] *}

### `JSONResponse` { #jsonresponse }

Takes some data and returns an `application/json` encoded response.

They are handled automatically by **FastAPI** and converted to JSON.

///

## Add custom headers { #add-custom-headers }

There are some situations in where it's useful to be able to add custom headers to the HTTP error. For example, for some types of security.

You probably won't need to use it directly in your code.

But in case you needed it for an advanced scenario, you can add custom headers:

Asynchronous code just means that the language 💬 has a way to tell the computer / program 🤖 that at some point in the code, it 🤖 will have to wait for *something else* to finish somewhere else. Let's say that *something else* is called "slow-file" 📝.

So, during that time, the computer can go and do some other work, while "slow-file" 📝 finishes.

**Spoiler alert**: il tutorial - Guida Utente include:

* Dichiarazione di **parameters** da altri posti diversi come: **headers**, **cookies**, **form fields** e **files**.
* Come stabilire **vincoli di validazione** come `maximum_length` o `regex`.