FastAPI

---

This is an example of an API written using python FastAPI framework and you can check some useful examples implemented here.

You can check the project running here: https://fastapi.ivanbicalho.com

Bootstrapping

FastAPI project is mainly an instance of FastAPI class. You can configure many settings when instantiating this class like title, description and so on.

You get Swagger and Redoc for free, just enabling at instance time, like:

app = FastAPI(
    title="API title",
    description="API Description",
    docs_url="/docs",  # Swagger, None to disable
    redoc_url="/redoc",  # Redoc, None to disable
)

Pydantic

FastAPI relies on pydantic library to data validation and also uses it in docs like Swagger

class UserRequest(BaseModel):  # BaseModel = pydantic base class
    name: str = Field(title="Name", description="User first name", example="Ivan")
    age: int = Field(title="Age", description="User age", example="22", gt=0)

Routes

Once you defined a FastAPI instance variable, in this case: app, we just need to define a simple decorator in a function to create a route:

@app.get("/users/{id}", summary="Get a specific user")
def get(id: int):
    user = user_repository.get(id)
    if not user:
        raise HTTPException(status.HTTP_404_NOT_FOUND, "Not found")
    return user

If your User type has a lot of fields and you only want to return a few fields, you can simply set a response_model and keep the function untouched, like:

class UserResponse(BaseModel):
    id: int
    name: str

@app.get("/users/{id}", summary="Get a specific user", response_model=UserResponse)
def get(id: int):
    ...

Dependency injection

FastAPI has a very powerful Dependency Injection system that is very useful when you need to:

• Have shared logic (the same code logic again and again).
• Share database connections.
• Enforce security, authentication, role requirements, etc.
• And many other things...

If you want to ensure that a request is protected and can only be accessed by a known user, you can define a structure like that:

def get_logged_username():
    # check for token existence in request header
    # parse and validate the token
    # extract and return the current user
    # if something goes wrong, raise an HTTP 401 exception
    ...

@app.get("/users/{id}", summary="Get a specific user", response_model=UserResponse)
def get(id: int, username: str = Depends(get_logged_username)):
    # this method will be executed only if we get a valid username
    ...

Run locally

Command to run locally: uvicorn python_module:instance_variable. You can also put the flag --reload to reload the project every time you make a change:

pip install uvicorn
uvicorn main:app --reload  # main.py -> app = FastAPI(...)

More info

You can find all the details in official documentation here.