Path and Query Parameters

from fastapi import FastAPI, Path

app = FastAPI()

# Basic — type inferred from annotation
@app.get("/items/{item_id}")
def get_item(item_id: int):
    return {"id": item_id}

# With validation via Path()
@app.get("/items/{item_id}")
def get_item(
    item_id: int = Path(
        ...,              # required (same as ...)
        title="Item ID",
        description="Must be >= 1",
        ge=1,
        le=1000,
    )
):
    return {"id": item_id}

from fastapi import Query

# Simple — any param NOT in the path string is a query param
@app.get("/items")
def list_items(skip: int = 0, limit: int = 10):
    return db[skip : skip + limit]

# Optional query param
from typing import Optional

@app.get("/items")
def list_items(q: Optional[str] = None):
    return {"q": q}

# With Query() metadata + validation
@app.get("/search")
def search(
    q: str = Query(
        default=...,          # required; use None for optional
        min_length=3,
        max_length=50,
        pattern=r"^\w+$",
        alias="query",        # URL uses ?query= but Python sees `q`
        title="Search term",
        description="Search the catalog",
        deprecated=False,
        include_in_schema=True,
    )
):
    return {"q": q}

from typing import List

@app.get("/items")
def list_items(tags: List[str] = Query(default=[])):
    # URL: /items?tags=a&tags=b&tags=c
    return {"tags": tags}

from fastapi import Header

@app.get("/items")
def get_items(user_agent: str = Header(default=None)):
    return {"User-Agent": user_agent}

# FastAPI auto-converts hyphens → underscores:
# X-Token header → x_token parameter
@app.get("/secure")
def secure(x_token: str = Header(...)):
    return {"token": x_token}

# Disable conversion:
@app.get("/raw")
def raw(accept_encoding: str = Header(default=None, convert_underscores=False)):
    ...

from fastapi import Cookie

@app.get("/me")
def get_me(session_id: str = Cookie(default=None)):
    return {"session": session_id}

@app.get("/users/{user_id}/items")
def user_items(
    user_id: int = Path(..., ge=1),
    skip: int = Query(default=0, ge=0),
    limit: int = Query(default=10, le=100),
    q: Optional[str] = None,
):
    return {"user": user_id, "skip": skip, "limit": limit, "q": q}

from enum import Enum

class ModelName(str, Enum):
    alexnet = "alexnet"
    resnet = "resnet"
    lenet = "lenet"

@app.get("/models/{model_name}")
def get_model(model_name: ModelName):
    if model_name is ModelName.alexnet:
        return {"model": model_name, "message": "Deep Learning FTW!"}
    return {"model": model_name}

# matches /files/home/user/report.pdf
@app.get("/files/{file_path:path}")
def read_file(file_path: str):
    return {"path": file_path}

# int, float, Decimal all work; FastAPI coerces from string
@app.get("/calc")
def calc(x: float = 0.0, n: int = 1):
    return x ** n

# Truthy: 1, true, on, yes  |  Falsy: 0, false, off, no  (case-insensitive)
@app.get("/items")
def list_items(active: bool = True):
    return {"active": active}