"description": "Successful Response",
                            "content": {"application/json": {"schema": {}}},
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

First, create the main, top-level, **FastAPI** application, and its *path operations*:

```Python hl_lines="3  6-8"
{!../../../docs_src/sub_applications/tutorial001.py!}
```

### Sub-application

Then, create your sub-application, and its *path operations*.

This sub-application is just another standard FastAPI application, but this is the one that will be "mounted":

```Python hl_lines="11  14-16"

# Bigger Applications - Multiple Files

If you are building an application or a web API, it's rarely the case that you can put everything on a single file.

**FastAPI** provides a convenience tool to structure your application while keeping all the flexibility.

!!! info
    If you come from Flask, this would be the equivalent of Flask's Blueprints.

## An example file structure

Let's say you have a file structure like this:

```
.
├── app

The client will get a **500 Internal Server Error** for that request, but the application will continue working for the next requests instead of just crashing completely.

### Bigger Errors - Crashes

Nevertheless, there might be cases where we write some code that **crashes the entire application** making Uvicorn and Python crash. 💥

# Global Dependencies

For some types of applications you might want to add dependencies to the whole application.

Similar to the way you can [add `dependencies` to the *path operation decorators*](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}, you can add them to the `FastAPI` application.

In that case, they will be applied to all the *path operations* in the application:

=== "Python 3.9+"

    ```Python hl_lines="16"

running on the server (the machine, host, etc.) and **managing all the HTTPS parts**: receiving the **encrypted HTTPS requests**, sending the **decrypted HTTP requests** to the actual HTTP application running in the same server (the **FastAPI** application, in this case), take the **HTTP response** from the application, **encrypt it** using the appropriate **HTTPS certificate** and sending it back to the client using **HTTPS**. This server is often called a **<a href="https://en.wikipedia.org/wiki/TL...

                            "description": "Successful Response",
                            "content": {"application/json": {"schema": {}}},
                        },
                        "422": {
                            "description": "Validation Error",
                            "content": {
                                "application/json": {
                                    "schema": {

    * A les meilleures performances, étant donné qu'il n'a pas beaucoup de code mis-à-part le serveur en lui-même.
    * On n'écrit pas une application avec uniquement Uvicorn. Cela signifie que le code devrait inclure plus ou moins, au minimum, tout le code offert par Starlette (ou **FastAPI**). Et si on fait cela, l'application finale apportera les mêmes complications que si on avait utilisé un framework et que l'on avait minimisé la quantité de code et de bugs.

                    "responses": {
                        "200": {
                            "description": "Successful Response",
                            "content": {
                                "application/json": {
                                    "schema": {
                                        "title": "Response Read Users Users  Get",
                                        "type": "array",

                    "responses": {
                        "200": {
                            "description": "Successful Response",
                            "content": {
                                "application/json": {
                                    "schema": {
                                        "title": "Response Read Users Users  Get",
                                        "type": "array",