FastAPI Parameters

Path parameter in decorator, gets executed wenn call is made to '/' with get method.

@app.get("/")
def read_root():
    return {"message": "Hello World"}

Path Parameters

Path variables are defined in the path of the decorator with {}.

@app.get("/items/{item_id}")
def read_item(item_id: int):
    return {"item_id": item_id}

Validation with Type Hints

@app.get("/items/{item_id}")
def read_item(item_id: int):
    return {"item_id": item_id}

• {item_id} = 1 results {"item_id": 1}
• {item_id} = "foo" results type_error.integer

Warning: Order matters

/users/me has to be defined before /users/{user_id}

Predefined Values

from enum import Enum

class Name(str, Enum):
    a = "a"
    b = "b"

@app.get("/models/{name}")
def get(name: Name):
    if name == Name.a:
        return {"name": name, "value": "a"}
    if name == Name.b:
        return {"name": name, "value": "b"}
    return {"name": name, "value": "unknown"}

Path Parameter Converter

Note

If the path has no other parameters {}, just the path use :path

@app.get("/files/{file_path:path}")
def read_file(file_path: str):
    return {"file_path": file_path}

Query Parameters

Other function parameters are interpreted as query parameters.

http://127.0.0.1:8000/items/?skip=0&limit=10

• ? starts query parameter list
• & separates query parameters

Default Query Parameters

@app.get("/items/")
def read_items(q: str = None):
    return {"q": q}

• q = None default value

Required Query Parameters

@app.get("/items/")
def read_items(q: str):
    return {"q": q}

• q is required

Optional Query Parameters

@app.get("/items/")
def read_items(q: str | None = None):
    return {"q": q}

• q = None is optional and default None

Multiple Path and Query Parameters

Info

FasAPI detects all path parameters and query parameters by name.

@app.get("/users/{user_id}/items/{item_id}")
def read_user_item(
    user_id: int, item_id: str, q: str | None = None, short: bool = False):
    ...
    return item

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