Hello World in FastApi | 2

Finally, it's time to create the "Hello World" with FastApi; that is, to implement the minimum necessary to be able to see something on the screen; so, we create a file inside the project (the tasks folder):

api.py

With the following code:

api.py

from fastapi import FastAPI
app = FastAPI()
@app.get("/")
def hello_world():
    return {"hello": "world"}

In this first example, the first thing we do is load a class that provides access to the FastAPI framework:

from fastapi import FastAPI

With this class, we create an instance of FastApi:

app = FastAPI ()

Which gives us access to multiple features of the framework, such as creating the application routes.

We define a GET request for the root and this is done through a decorator like the one we can see below:

@app.get("/")

Of course, we can access other types of requests such as POST, PUT, PATCH or DELETE indicating the corresponding method which has its direct equivalent with the name of the request to use; that is, to send a GET request, we use the function get(), to send a POST request, we use the post() function.

As with other web frameworks, each request is processed by a function, in the previous example, the GET request for the root is processed by a function called hello_world() which all it does is return a dictionary indicating the "hello world" message:

@app.get("/")
def hello_world():
    return {"hello": "world"}

With this, we have our first hello world example in FlastApi; but, in order to see this message on the screen, specifically any program that allows processing HTTP requests such as a browser, we have to open the server associated with the previous application and this is where we use the previously installed uvicorn server; to do this, from the terminal and root of the project, we use the following command:

$ uvicorn api: app --reload

With the previous command, we indicate the name of the file, which in this case is called api.py:

api:app

And that the server stays tuned for changes; that is, with the option of:

--reload

The server will be reloaded every time changes are made to the application.

When executing the previous command, we will see in the terminal:

INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [15820] using StatReload
INFO:     Started server process [4024]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     127.0.0.1:58209 - "GET / HTTP/1.1" 200 OK
INFO:     127.0.0.1:58209 - "GET /favicon.ico HTTP/1.1" 404 Not Found
INFO:     127.0.0.1:58209 - "GET / HTTP/1.1" 200 OK

It tells us which is the route in which the application has been raised:

http://127.0.0.1:8000

And from this route, which we can execute in the browser, we will see the message of:

http://127.0.0.1:8000
{
  "hello": "world"
}

If necessary, you can also customize the port using the port option and indicate the port you want to use, in this example, port 8001:

$ uvicorn api:app --port 8001

With the reload option:

$ uvicorn api:app --port 8001 --reload

And in the output you will now see that the server is loading the application on port 8001

Uvicorn running on http://127.0.0.1:8001 (Press CTRL+C to quit)

Finally, the previous function can also indicate the return data type:

@app.get("/")
def hello_world() -> dict:
    return {"hello": "world"}

It is important to note that a GET type request is used, which is the typical type of request used to query data; and the only one that we can use directly from the browser without having to use a form.

07-11-2023 - Andrés Cruz

En español

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