## Table 1: Core Application Setup | **Concept** | **Example** | **Description** | |---|---|---| | [**FastAPI app instance**](https://fastapi.tiangolo.com/tutorial/first-steps/) | `app = FastAPI()`
`app = FastAPI(title="My API", version="1.0.0")` | • Creates the main application instance
• accepts optional **metadata** like title, description, version for OpenAPI docs. | | [**Path operation decorator**](https://fastapi.tiangolo.com/tutorial/first-steps/) | `@app.get("/")`
`@app.post("/items")` | • Defines an **HTTP endpoint** with method and path
• decorator tells FastAPI to handle requests to this route. | | [**Path operation function**](https://fastapi.tiangolo.com/tutorial/first-steps/) | `def read_root():`
` return {"msg": "Hello"}` | • Function executed when endpoint is hit
• **return value is automatically serialized** to JSON. | | [**Run with Uvicorn**](https://fastapi.tiangolo.com/tutorial/first-steps/) | `uvicorn main:app --reload` | • Starts the **ASGI server** to run FastAPI
• `--reload` enables auto-restart during development. | | [**Async path operation**](https://fastapi.tiangolo.com/async/) | `async def read_items():`
` return await db.fetch()` | • Uses `async def` for **non-blocking I/O operations**
• better performance for I/O-bound tasks. | | [**Lifespan context manager**](https://fastapi.tiangolo.com/advanced/events/) | `@asynccontextmanager`
`async def lifespan(app):`
` # startup`
` yield`
` # shutdown` | • Manages **startup and shutdown** logic
• replaces deprecated `on_event` decorators with single context manager. | | [**Automatic documentation**](https://fastapi.tiangolo.com/tutorial/first-steps/) | `/docs` for Swagger UI
`/redoc` for ReDoc | • FastAPI **auto-generates interactive API docs** at these endpoints based on your code
• requires zero configuration. | | [**Pydantic integration**](https://fastapi.tiangolo.com/tutorial/body/) | `class Item(BaseModel):`
` name: str`
` price: float` | • Pydantic models provide **automatic validation and serialization**
• FastAPI uses them for request/response schemas. | ## Table 2: HTTP Methods and Route Definitions | **Method** | **Example** | **Description** | |---|---|---| | [**GET request**](https://fastapi.tiangolo.com/tutorial/first-steps/) | `@app.get("/items/{id}")`
`def read_item(id: int):` | • Retrieves data
• **no request body**, typically uses path or query parameters. | | [**POST request**](https://fastapi.tiangolo.com/tutorial/body/) | `@app.post("/items")`
`def create_item(item: Item):` | • Creates new resource
• accepts **request body** defined by Pydantic model. | | [**PUT request**](https://fastapi.tiangolo.com/tutorial/body/) | `@app.put("/items/{id}")`
`def update_item(id: int, item: Item):` | • Replaces entire resource
• expects **complete object** in request body. | | [**PATCH request**](https://fastapi.tiangolo.com/tutorial/body/) | `@app.patch("/items/{id}")`
`def partial_update(id: int, item: PartialItem):` | • Updates **partial resource**
• only specified fields are modified. | | [**DELETE request**](https://fastapi.tiangolo.com/tutorial/first-steps/) | `@app.delete("/items/{id}")`
`def delete_item(id: int):` | • Removes resource
• typically returns **status confirmation**. | | [**HEAD request**](https://fastapi.tiangolo.com/reference/fastapi/) | `@app.head("/items")`
`def items_head():` | • Returns headers only, **no body**
• useful for checking resource existence or metadata. | | [**OPTIONS request**](https://fastapi.tiangolo.com/reference/fastapi/) | `@app.options("/items")`
`def items_options():` | • Returns **allowed HTTP methods** for endpoint
• often handled automatically for CORS. | ## Table 3: Request Parameters | **Type** | **Example** | **Description** | |---|---|---| | [**Path parameter**](https://fastapi.tiangolo.com/tutorial/path-params/) | `@app.get("/items/{item_id}")`
`def read(item_id: int):` | • Extracts value from URL path
• **type validated automatically** based on annotation. | | [**Query parameter**](https://fastapi.tiangolo.com/tutorial/query-params/) | `def read_items(skip: int = 0, limit: int = 10):` | • Reads from URL query string (`?skip=0&limit=10`)
• **optional with defaults**. | | [**Request body**](https://fastapi.tiangolo.com/tutorial/body/) | `def create(item: Item):` | • Accepts JSON payload
• **Pydantic model validates** structure and types automatically. | | [**Multiple body parameters**](https://fastapi.tiangolo.com/tutorial/body-multiple-params/) | `def create(item: Item, user: User):` | • Accepts **multiple JSON objects** in request body
• FastAPI expects nested structure. | | [**Header parameter**](https://fastapi.tiangolo.com/tutorial/header-params/) | `from fastapi import Header`
`def read(user_agent: str = Header()):` | • Reads HTTP headers
• automatically converts **hyphen-case to snake_case**. | | [**Cookie parameter**](https://fastapi.tiangolo.com/tutorial/cookie-params/) | `from fastapi import Cookie`
`def read(session_id: str = Cookie()):` | • Extracts cookie values
• **type-validated** like other parameters. | | [**Form data**](https://fastapi.tiangolo.com/tutorial/request-forms/) | `from fastapi import Form`
`def login(username: str = Form()):` | • Accepts `application/x-www-form-urlencoded`
• requires **python-multipart** installed. | | [**File upload**](https://fastapi.tiangolo.com/tutorial/request-files/) | `from fastapi import UploadFile`
`def upload(file: UploadFile):` | • Handles file uploads
• `UploadFile` provides **async methods** and metadata like filename. | | [**Multiple file upload**](https://fastapi.tiangolo.com/tutorial/request-files/) | `def upload(files: list[UploadFile]):` | • Accepts **multiple files** in single request
• validated as list. | ## Table 4: Parameter Validation | **Technique** | **Example** | **Description** | |---|---|---| | [**Query validation**](https://fastapi.tiangolo.com/tutorial/query-params-str-validations/) | `from fastapi import Query`
`q: str = Query(min_length=3)` | Applies **constraints** like min/max length, regex patterns to query parameters. | | [**Path validation**](https://fastapi.tiangolo.com/tutorial/path-params-numeric-validations/) | `from fastapi import Path`
`id: int = Path(ge=1, le=1000)` | Validates path parameters with **numeric constraints** like ge (greater/equal), le (less/equal). | | [**Required query parameter**](https://fastapi.tiangolo.com/tutorial/query-params-str-validations/) | `q: str = Query(...)` | • Ellipsis `...` makes optional parameter **required**
• alternative to default value. | | [**Optional with None**](https://fastapi.tiangolo.com/tutorial/query-params/) | `q: str | None = None` | • Python 3.10+ union syntax for **optional parameters**
• older versions use `Optional[str]`. | | [**List query parameter**](https://fastapi.tiangolo.com/tutorial/query-params-str-validations/) | `tags: list[str] = Query([])` | • Accepts **multiple values** for same parameter (`?tags=a&tags=b`)
• validated as list. | | [**Alias parameter**](https://fastapi.tiangolo.com/tutorial/query-params-str-validations/) | `item_query: str = Query(alias="item-query")` | Maps **hyphenated URL param** to snake_case Python variable. | | [**Deprecated parameter**](https://fastapi.tiangolo.com/tutorial/query-params-str-validations/) | `old_param: str = Query(deprecated=True)` | • Marks parameter as **deprecated** in OpenAPI docs
• still functional but discouraged. | | [**Regex validation**](https://fastapi.tiangolo.com/tutorial/query-params-str-validations/) | `code: str = Query(pattern="^[A-Z]{3}$")` | Validates string parameter against **regex pattern**. | | [**Numeric constraints**](https://fastapi.tiangolo.com/tutorial/path-params-numeric-validations/) | `price: float = Query(gt=0, le=9999.99)` | Applies **gt** (greater than), **lt** (less than), **ge**, **le** constraints to numbers. | ## Table 5: Pydantic Models and Validation | **Concept** | **Example** | **Description** | |---|---|---| | [**BaseModel**](https://docs.pydantic.dev/latest/concepts/models/) | `class Item(BaseModel):`
` name: str`
` price: float` | • Base class for all Pydantic models
• provides **automatic validation and serialization**. | | [**Field constraints**](https://docs.pydantic.dev/latest/concepts/fields/) | `from pydantic import Field`
`price: float = Field(gt=0)` | • Adds **validation rules** directly to model fields
• similar to Query/Path but for models. | | [**Field description**](https://docs.pydantic.dev/latest/concepts/fields/) | `name: str = Field(description="Item name")` | • Adds **documentation** to field
• appears in OpenAPI schema. | | [**Field example**](https://docs.pydantic.dev/latest/concepts/fields/) | `price: float = Field(examples=[9.99, 19.99])` | Provides **example values** for API documentation and testing. | | [**Field validator**](https://docs.pydantic.dev/latest/concepts/validators/) | `@field_validator('email')`
`def check_email(cls, v):` | • Custom **validation logic** for specific field
• runs after type validation. | | [**Model validator**](https://docs.pydantic.dev/latest/concepts/validators/) | `@model_validator(mode='after')`
`def check_passwords(self):` | • Validates **entire model** after individual fields
• useful for cross-field validation. | | [**Config class**](https://docs.pydantic.dev/latest/concepts/config/) | `class Config:`
` str_strip_whitespace = True` | • Customizes **model behavior**
• settings like schema_extra, alias generation. | | [**Optional fields**](https://docs.pydantic.dev/latest/concepts/models/) | `description: str | None = None` | • Field can be **omitted or null**
• uses Python union type or `Optional`. | | [**Computed field**](https://docs.pydantic.dev/latest/concepts/fields/) | `@computed_field`
`@property`
`def total(self) -> float:` | • Adds **calculated field** to model
• included in serialization but not validation. | | [**Model inheritance**](https://docs.pydantic.dev/latest/concepts/models/) | `class ExtendedItem(Item):`
` category: str` | • Inherits fields from base model
• enables **model reuse and extension**. | ## Table 6: Response Configuration | **Technique** | **Example** | **Description** | |---|---|---| | [**Response model**](https://fastapi.tiangolo.com/tutorial/response-model/) | `@app.post("/items", response_model=Item)` | • Specifies **return type** for validation and docs
• filters response to match model. | | [**Response model exclude**](https://fastapi.tiangolo.com/tutorial/response-model/) | `response_model=User, response_model_exclude={"password"}` | • **Removes specified fields** from response
• useful for hiding sensitive data. | | [**Status code**](https://fastapi.tiangolo.com/tutorial/response-status-code/) | `@app.post("/items", status_code=201)` | • Sets **HTTP status code** for response
• default is 200 for GET, 201 for POST recommended. | | [**JSONResponse**](https://fastapi.tiangolo.com/advanced/custom-response/) | `from fastapi.responses import JSONResponse`
`return JSONResponse(content=data)` | Explicit **JSON response** with custom headers or status code. | | [**HTMLResponse**](https://fastapi.tiangolo.com/advanced/custom-response/) | `from fastapi.responses import HTMLResponse`
`return HTMLResponse(content=html)` | • Returns **HTML content**
• sets Content-Type to text/html. | | [**RedirectResponse**](https://fastapi.tiangolo.com/advanced/custom-response/) | `from fastapi.responses import RedirectResponse`
`return RedirectResponse(url="/new")` | • **HTTP redirect** to different URL
• status_code defaults to 307. | | [**FileResponse**](https://fastapi.tiangolo.com/advanced/custom-response/) | `from fastapi.responses import FileResponse`
`return FileResponse(path="file.pdf")` | • Serves **static files**
• handles content-type and download headers automatically. | | [**StreamingResponse**](https://fastapi.tiangolo.com/advanced/custom-response/) | `from fastapi.responses import StreamingResponse`
`return StreamingResponse(generator)` | • Streams **large data** in chunks
• memory-efficient for big responses. | | [**ORJSONResponse**](https://fastapi.tiangolo.com/advanced/custom-response/) | `from fastapi.responses import ORJSONResponse`
`return ORJSONResponse(content=data)` | • Uses **faster orjson library** for JSON serialization
• 2-3x performance improvement. | | [**Response headers**](https://fastapi.tiangolo.com/advanced/response-headers/) | `from fastapi import Response`
`response.headers["X-Custom"] = "value"` | Sets **custom HTTP headers** in response. | | [**Set cookies**](https://fastapi.tiangolo.com/advanced/response-cookies/) | `response.set_cookie(key="session", value="abc")` | • Adds **cookie to response**
• supports httponly, secure, samesite options. | ## Table 7: Dependency Injection | **Pattern** | **Example** | **Description** | |---|---|---| | [**Basic dependency**](https://fastapi.tiangolo.com/tutorial/dependencies/) | `def get_db():`
` return db`

`def route(db = Depends(get_db)):` | • Function providing **reusable logic**
• injected via `Depends()`. | | [**Async dependency**](https://fastapi.tiangolo.com/tutorial/dependencies/) | `async def get_session():`
` async with Session() as s:`
` yield s` | • **Async generator** dependency
• cleanup happens after response using `yield`. | | [**Class dependency**](https://fastapi.tiangolo.com/advanced/advanced-dependencies/) | `class Pagination:`
` def __init__(self, skip=0):` | • Class instances as dependencies
• `__init__` parameters become **sub-dependencies**. | | [**Nested dependencies**](https://fastapi.tiangolo.com/tutorial/dependencies/) | `def get_user(token = Depends(get_token)):` | • Dependency can **depend on other dependencies**
• creates dependency chain. | | [**Global dependencies**](https://fastapi.tiangolo.com/tutorial/dependencies/) | `app = FastAPI(dependencies=[Depends(verify)])` | • Applied to **all routes** in application
• useful for auth, logging. | | [**Router dependencies**](https://fastapi.tiangolo.com/tutorial/bigger-applications/) | `router = APIRouter(dependencies=[Depends(check)])` | • Applied to **all routes in router**
• scoped to specific module. | | [**Yield dependency**](https://fastapi.tiangolo.com/tutorial/dependencies/) | `def get_db():`
` db = Database()`
` yield db`
` db.close()` | • Provides **resource cleanup** after request
• code after yield runs as teardown. | | [**Dependency override**](https://fastapi.tiangolo.com/advanced/testing-dependencies/) | `app.dependency_overrides[get_db] = mock_db` | • Replaces dependency for **testing**
• allows mocking without changing code. | | [**Dependencies in path decorator**](https://fastapi.tiangolo.com/tutorial/dependencies/) | `@app.get("/items", dependencies=[Depends(verify)])` | • Dependency **executed but result not used** in function
• for side effects only. | ## Table 8: Error Handling | **Approach** | **Example** | **Description** | |---|---|---| | [**HTTPException**](https://fastapi.tiangolo.com/tutorial/handling-errors/) | `from fastapi import HTTPException`
`raise HTTPException(status_code=404, detail="Not found")` | • **Built-in exception** for HTTP errors
• automatically formatted as JSON response. | | [**Custom exception**](https://fastapi.tiangolo.com/tutorial/handling-errors/) | `class CustomError(Exception):`
` pass` | • Define **custom exception class**
• can add custom handler. | | [**Exception handler**](https://fastapi.tiangolo.com/tutorial/handling-errors/) | `@app.exception_handler(CustomError)`
`def handler(request, exc):` | • Catches **specific exception type** globally
• returns custom response. | | [**Validation error handler**](https://fastapi.tiangolo.com/tutorial/handling-errors/) | `from fastapi.exceptions import RequestValidationError`
`@app.exception_handler(RequestValidationError)` | Customizes **Pydantic validation error** response format. | | [**Status code in exception**](https://fastapi.tiangolo.com/tutorial/handling-errors/) | `raise HTTPException(status_code=403, detail="Forbidden")` | • Sets **HTTP status code** directly in exception
• common codes: 400, 401, 403, 404, 500. | | [**Custom headers in exception**](https://fastapi.tiangolo.com/tutorial/handling-errors/) | `raise HTTPException(status_code=401, headers={"WWW-Authenticate": "Bearer"})` | • Adds **custom headers** to error response
• useful for auth challenges. | | [**Override default handlers**](https://fastapi.tiangolo.com/tutorial/handling-errors/) | `from starlette.exceptions import HTTPException as StarletteHTTPException`
`@app.exception_handler(StarletteHTTPException)` | Replaces **FastAPI's default error formatting**. | ## Table 9: Authentication and Security | **Mechanism** | **Example** | **Description** | |---|---|---| | [**OAuth2 password flow**](https://fastapi.tiangolo.com/tutorial/security/oauth2-jwt/) | `from fastapi.security import OAuth2PasswordBearer`
`oauth2 = OAuth2PasswordBearer(tokenUrl="token")` | • **Standard OAuth2 flow** for password-based authentication
• extracts token from Authorization header. | | [**OAuth2 password request**](https://fastapi.tiangolo.com/tutorial/security/oauth2-jwt/) | `from fastapi.security import OAuth2PasswordRequestForm`
`def login(form: OAuth2PasswordRequestForm = Depends()):` | • **Form data model** for username/password login
• includes username, password, optional scope. | | [**API key in header**](https://fastapi.tiangolo.com/tutorial/security/api-keys/) | `from fastapi.security import APIKeyHeader`
`api_key = APIKeyHeader(name="X-API-Key")` | • Extracts **API key from custom header**
• name specifies header name. | | [**API key in query**](https://fastapi.tiangolo.com/tutorial/security/api-keys/) | `from fastapi.security import APIKeyQuery`
`api_key = APIKeyQuery(name="api_key")` | • Reads **API key from query parameter**
• less secure than header. | | [**API key in cookie**](https://fastapi.tiangolo.com/tutorial/security/api-keys/) | `from fastapi.security import APIKeyCookie`
`api_key = APIKeyCookie(name="session")` | Extracts **API key from cookie**. | | [**JWT token creation**](https://fastapi.tiangolo.com/tutorial/security/oauth2-jwt/) | `from jose import jwt`
`token = jwt.encode(data, SECRET, algorithm="HS256")` | • **Encodes JWT token** with payload and secret
• requires python-jose library. | | [**JWT token verification**](https://fastapi.tiangolo.com/tutorial/security/oauth2-jwt/) | `from jose import JWTError, jwt`
`payload = jwt.decode(token, SECRET, algorithms=["HS256"])` | • **Decodes and verifies JWT**
• raises JWTError if invalid. | | [**Password hashing**](https://fastapi.tiangolo.com/tutorial/security/oauth2-jwt/) | `from passlib.context import CryptContext`
`pwd_context = CryptContext(schemes=["bcrypt"])` | • **Hashes passwords** with bcrypt
• never store plain passwords. | | [**Current user dependency**](https://fastapi.tiangolo.com/tutorial/security/oauth2-jwt/) | `async def get_current_user(token = Depends(oauth2)):`
` # decode token, fetch user` | • Dependency that **extracts and validates user** from token
• reusable across routes. | | [**Security scopes**](https://fastapi.tiangolo.com/advanced/security/oauth2-scopes/) | `@app.get("/items", dependencies=[Depends(has_scope("read:items"))])` | • **Permission-based access control**
• validates OAuth2 scopes. | ## Table 10: Middleware | **Type** | **Example** | **Description** | |---|---|---| | [**CORS middleware**](https://fastapi.tiangolo.com/tutorial/cors/) | `from fastapi.middleware.cors import CORSMiddleware`
`app.add_middleware(CORSMiddleware, allow_origins=["*"])` | • Enables **Cross-Origin Resource Sharing**
• configures which domains can access API. | | [**Custom function middleware**](https://fastapi.tiangolo.com/advanced/middleware/) | `@app.middleware("http")`
`async def add_header(request, call_next):` | • **Function-based middleware**
• runs before and after every request. | | [**Custom class middleware**](https://fastapi.tiangolo.com/advanced/middleware/) | `class TimingMiddleware(BaseHTTPMiddleware):`
` async def dispatch(self, request, call_next):` | • **Class-based middleware**
• more complex logic, state management. | | [**Trusted host middleware**](https://fastapi.tiangolo.com/advanced/middleware/) | `from starlette.middleware.trustedhost import TrustedHostMiddleware`
`app.add_middleware(TrustedHostMiddleware, allowed_hosts=["*.example.com"])` | • Validates **Host header**
• prevents HTTP Host header attacks. | | [**HTTPS redirect middleware**](https://fastapi.tiangolo.com/advanced/middleware/) | `from starlette.middleware.httpsredirect import HTTPSRedirectMiddleware`
`app.add_middleware(HTTPSRedirectMiddleware)` | • **Redirects HTTP to HTTPS**
• enforces secure connections. | | [**GZip middleware**](https://fastapi.tiangolo.com/advanced/middleware/) | `from fastapi.middleware.gzip import GZipMiddleware`
`app.add_middleware(GZipMiddleware, minimum_size=1000)` | • **Compresses responses** over specified size
• reduces bandwidth. | | [**Session middleware**](https://www.starlette.io/middleware/) | `from starlette.middleware.sessions import SessionMiddleware`
`app.add_middleware(SessionMiddleware, secret_key="key")` | Adds **session support** via signed cookies. | ## Table 11: Background Tasks | **Approach** | **Example** | **Description** | |---|---|---| | [**BackgroundTasks**](https://fastapi.tiangolo.com/tutorial/background-tasks/) | `from fastapi import BackgroundTasks`
`def task(email: str):`
` send_email(email)` | • **Simple background function** executed after response
• no external queue needed. | | [**Add background task**](https://fastapi.tiangolo.com/tutorial/background-tasks/) | `def endpoint(bg: BackgroundTasks):`
` bg.add_task(send_email, to="user@example.com")` | • Schedules function to run **after response sent**
• tasks run in same process. | | [**Multiple background tasks**](https://fastapi.tiangolo.com/tutorial/background-tasks/) | `bg.add_task(task1)`
`bg.add_task(task2)` | **Multiple tasks run sequentially** in order added. | | [**Background task with dependencies**](https://fastapi.tiangolo.com/tutorial/background-tasks/) | `def task(db = Depends(get_db)):` | • Background task can use **dependency injection**
• dependencies resolved when task runs. | | [**Celery integration**](https://testdriven.io/courses/fastapi-celery/intro/) | `from celery import Celery`
`celery = Celery("tasks", broker="redis://localhost")`
`@celery.task`
`def heavy_task():` | • **Distributed task queue** for heavy/long-running jobs
• runs in separate workers outside request cycle. | | [**ARQ for async tasks**](https://davidmuraya.com/blog/fastapi-background-tasks-arq-vs-built-in/) | `from arq import create_pool`
`redis = await create_pool()` | • **Redis-based async task queue**
• alternative to Celery for async-first applications. | ## Table 12: Database Integration | **Technique** | **Example** | **Description** | |---|---|---| | [**SQLAlchemy async session**](https://fastapi.tiangolo.com/tutorial/sql-databases/) | `from sqlalchemy.ext.asyncio import AsyncSession`
`async def get_db():`
` yield session` | • **Async database session** for non-blocking DB operations
• requires async driver. | | [**SQLAlchemy sync session**](https://fastapi.tiangolo.com/tutorial/sql-databases/) | `from sqlalchemy.orm import Session`
`def get_db():`
` yield db` | • **Synchronous session**
• simpler but blocks during queries. | | [**Database model**](https://fastapi.tiangolo.com/tutorial/sql-databases/) | `from sqlalchemy import Column, Integer, String`
`class User(Base):`
` id = Column(Integer, primary_key=True)` | • **ORM model** defining table structure
• SQLAlchemy maps to database tables. | | [**Async database query**](https://docs.sqlalchemy.org/en/20/orm/extensions/asyncio.html) | `result = await session.execute(select(User))`
`users = result.scalars().all()` | • Executes **async query**
• uses SQLAlchemy 2.0 style. | | [**Database dependency**](https://fastapi.tiangolo.com/tutorial/sql-databases/) | `def endpoint(db: Session = Depends(get_db)):` | • Injects **database session** into route
• session closed automatically after request. | | [**Alembic migrations**](https://alembic.sqlalchemy.org/en/latest/) | `alembic init alembic`
`alembic revision --autogenerate`
`alembic upgrade head` | • **Database schema migrations**
• tracks and applies schema changes over time. | | [**Connection pooling**](https://docs.sqlalchemy.org/en/20/core/pooling.html) | `engine = create_async_engine(url, pool_size=20, max_overflow=10)` | • **Reuses database connections**
• critical for production performance. | ## Table 13: WebSockets and Real-Time Communication | **Feature** | **Example** | **Description** | |---|---|---| | [**WebSocket endpoint**](https://fastapi.tiangolo.com/advanced/websockets/) | `from fastapi import WebSocket`
`@app.websocket("/ws")`
`async def websocket_endpoint(websocket: WebSocket):` | • Defines **WebSocket route**
• full-duplex communication channel. | | [**Accept connection**](https://fastapi.tiangolo.com/advanced/websockets/) | `await websocket.accept()` | • **Establishes WebSocket connection**
• must be called before send/receive. | | [**Receive message**](https://fastapi.tiangolo.com/advanced/websockets/) | `data = await websocket.receive_text()`
`data = await websocket.receive_json()` | • **Reads message** from client
• supports text, JSON, or bytes. | | [**Send message**](https://fastapi.tiangolo.com/advanced/websockets/) | `await websocket.send_text("Hello")`
`await websocket.send_json({"msg": "Hi"})` | **Sends message** to client. | | [**WebSocket disconnect**](https://fastapi.tiangolo.com/advanced/websockets/) | `try:`
` while True:`
` await websocket.receive_text()`
`except WebSocketDisconnect:` | • Handles **client disconnect**
• exception raised when connection closes. | | [**Server-Sent Events**](https://towardsdatascience.com/introducing-server-sent-events-in-python/) | `from fastapi.responses import StreamingResponse`
`def event_stream():`
` yield f"data: {msg}\n\n"` | • **One-way streaming** from server to client
• simpler than WebSockets for uni-directional updates. | ## Table 14: Testing | **Tool** | **Example** | **Description** | |---|---|---| | [**TestClient**](https://fastapi.tiangolo.com/tutorial/testing/) | `from fastapi.testclient import TestClient`
`client = TestClient(app)`
`response = client.get("/")` | • **Synchronous test client**
• tests FastAPI without running server. | | [**Test with pytest**](https://fastapi.tiangolo.com/tutorial/testing/) | `def test_read_main():`
` response = client.get("/")`
` assert response.status_code == 200` | • Standard **pytest patterns** work with TestClient
• uses fixtures for setup. | | [**TestClient as context manager**](https://fastapi.tiangolo.com/advanced/testing-events/) | `with TestClient(app) as client:`
` response = client.get("/")` | • **Triggers lifespan events** during testing
• startup/shutdown run automatically. | | [**Async test client**](https://www.starlette.io/testclient/) | `from httpx import AsyncClient`
`async with AsyncClient(app=app) as client:`
` response = await client.get("/")` | • **Async testing** with httpx
• required for testing async dependencies properly. | | [**Override dependency**](https://fastapi.tiangolo.com/advanced/testing-dependencies/) | `app.dependency_overrides[get_db] = lambda: mock_db` | • **Replaces real dependency** with mock for testing
• no code changes needed. | | [**Test file upload**](https://fastapi.tiangolo.com/tutorial/request-files/) | `files = {"file": ("test.txt", b"content", "text/plain")}`
`client.post("/upload", files=files)` | • **Simulates file upload** in tests
• tuple format: (filename, content, content-type). | | [**Test with pytest fixtures**](https://fastapi.tiangolo.com/tutorial/testing/) | `@pytest.fixture`
`def client():`
` return TestClient(app)` | • **Reusable test setup**
• pytest fixture creates client for all tests. | ## Table 15: Advanced Routing | **Concept** | **Example** | **Description** | |---|---|---| | [**APIRouter**](https://fastapi.tiangolo.com/tutorial/bigger-applications/) | `from fastapi import APIRouter`
`router = APIRouter(prefix="/items", tags=["items"])` | • **Modular routing**
• groups related endpoints with shared prefix and tags. | | [**Include router**](https://fastapi.tiangolo.com/tutorial/bigger-applications/) | `app.include_router(router)` | • **Mounts router** to main app
• enables splitting large apps into modules. | | [**Sub-application mounting**](https://fastapi.tiangolo.com/advanced/sub-applications/) | `app.mount("/v1", app_v1)` | • **Mounts independent FastAPI app** at path
• useful for API versioning. | | [**Static files**](https://fastapi.tiangolo.com/tutorial/static-files/) | `from fastapi.staticfiles import StaticFiles`
`app.mount("/static", StaticFiles(directory="static"))` | Serves **static files** from directory. | | [**Router dependencies**](https://fastapi.tiangolo.com/tutorial/bigger-applications/) | `router = APIRouter(dependencies=[Depends(verify_token)])` | • Applies **dependency to all routes** in router
• cleaner than per-route. | | [**Router tags**](https://fastapi.tiangolo.com/tutorial/bigger-applications/) | `router = APIRouter(tags=["items"])` | • Groups endpoints in **OpenAPI docs**
• creates collapsible sections. | | [**Route priority**](https://fastapi.tiangolo.com/tutorial/path-params/) | Define **more specific routes first**:
`@app.get("/users/me")`
`@app.get("/users/{id}")` | • FastAPI matches **first matching route**
• specific paths before parameterized ones. | ## Table 16: OpenAPI Customization | **Element** | **Example** | **Description** | |---|---|---| | [**Metadata**](https://fastapi.tiangolo.com/tutorial/metadata/) | `app = FastAPI(title="My API", description="Docs", version="1.0")` | Sets **API title, description, version** in OpenAPI schema and docs. | | [**Tags metadata**](https://fastapi.tiangolo.com/tutorial/metadata/) | `tags_metadata = [{"name": "items", "description": "Item operations"}]`
`app = FastAPI(openapi_tags=tags_metadata)` | Adds **descriptions to tag groups** in documentation. | | [**Custom OpenAPI schema**](https://fastapi.tiangolo.com/how-to/extending-openapi/) | `def custom_openapi():`
` # modify schema`
`app.openapi = custom_openapi` | • **Overrides OpenAPI generation**
• add custom extensions or modify schema. | | [**Disable docs**](https://fastapi.tiangolo.com/tutorial/metadata/) | `app = FastAPI(docs_url=None, redoc_url=None)` | • **Hides documentation** endpoints
• use in production if needed. | | [**Custom docs URL**](https://fastapi.tiangolo.com/tutorial/metadata/) | `app = FastAPI(docs_url="/api/docs")` | Changes **Swagger UI path** from default `/docs`. | | [**Operation ID**](https://fastapi.tiangolo.com/advanced/path-operation-advanced-configuration/) | `@app.get("/items", operation_id="get_all_items")` | • Sets **unique operation identifier** in OpenAPI
• useful for code generation tools. | | [**Deprecate endpoint**](https://fastapi.tiangolo.com/advanced/path-operation-advanced-configuration/) | `@app.get("/old", deprecated=True)` | • Marks endpoint as **deprecated** in docs
• still functional. | | [**Response examples**](https://fastapi.tiangolo.com/advanced/additional-responses/) | `responses={200: {"description": "OK", "content": {"application/json": {"example": {...}}}}}` | Adds **example responses** to OpenAPI docs. | | [**Configure Swagger UI**](https://fastapi.tiangolo.com/how-to/configure-swagger-ui/) | `app = FastAPI(swagger_ui_parameters={"defaultModelsExpandDepth": -1})` | Customizes **Swagger UI behavior** like theme, syntax highlighting, model expansion. | ## Table 17: Settings and Configuration | **Technique** | **Example** | **Description** | |---|---|---| | [**Pydantic Settings**](https://fastapi.tiangolo.com/advanced/settings/) | `from pydantic_settings import BaseSettings`
`class Settings(BaseSettings):`
` api_key: str` | • **Type-safe configuration** from environment variables
• validates config at startup. | | [**Read .env file**](https://fastapi.tiangolo.com/advanced/settings/) | `class Settings(BaseSettings):`
` class Config:`
` env_file = ".env"` | • Loads **environment variables from .env**
• requires python-dotenv. | | [**Settings dependency**](https://fastapi.tiangolo.com/advanced/settings/) | `def get_settings():`
` return Settings()`

`settings: Settings = Depends(get_settings)` | • **Injects settings** into routes
• enables easy mocking in tests. | | [**Cached settings**](https://fastapi.tiangolo.com/advanced/settings/) | `@lru_cache`
`def get_settings():`
` return Settings()` | • **Loads settings once** and caches
• improves performance. | | [**Multiple environments**](https://docs.pydantic.dev/latest/concepts/pydantic_settings/) | `class Settings(BaseSettings):`
` env: str = "dev"`
` database_url: str` | • Uses different **config per environment**
• set via ENV variable. | ## Table 18: Performance Optimization | **Strategy** | **Example** | **Description** | |---|---|---| | [**Async operations**](https://fastapi.tiangolo.com/async/) | `async def fetch_data():`
` return await http_client.get(url)` | • Use `async def` for **I/O-bound operations**
• enables concurrent request handling. | | [**Redis caching**](https://medium.com/@kirant3ja/redis-hybrid-caching-in-fastapi-af0bf0ec40cb) | `from fastapi_cache import FastAPICache`
`from fastapi_cache.backends.redis import RedisBackend`
`@cache(expire=60)` | • **Caches responses** in Redis
• reduces database load for repeated queries. | | [**Response caching headers**](https://mojoauth.com/implement-caching/implement-caching-with-fastapi) | `@app.get("/", response_headers={"Cache-Control": "max-age=3600"})` | • Sets **HTTP caching headers**
• clients/proxies cache responses. | | [**Connection pooling**](https://docs.sqlalchemy.org/en/20/core/pooling.html) | `engine = create_engine(url, pool_size=20)` | • **Reuses database connections**
• critical for high-throughput APIs. | | [**ORJSONResponse**](https://fastapi.tiangolo.com/advanced/custom-response/) | `app = FastAPI(default_response_class=ORJSONResponse)` | • Uses **faster JSON library**
• 2-3x performance improvement over standard json. | | [**Uvicorn workers**](https://www.uvicorn.org/deployment/) | `uvicorn main:app --workers 4` | • Runs **multiple worker processes**
• utilizes multiple CPU cores. | | [**Gunicorn + Uvicorn**](https://www.uvicorn.org/deployment/) | `gunicorn main:app --workers 4 --worker-class uvicorn.workers.UvicornWorker` | • **Process manager** with Uvicorn workers
• production-grade deployment. | ## Table 19: Advanced Patterns | **Pattern** | **Example** | **Description** | |---|---|---| | [**GraphQL integration**](https://strawberry.rocks/docs/integrations/fastapi) | `from strawberry.fastapi import GraphQLRouter`
`app.include_router(GraphQLRouter(schema), prefix="/graphql")` | • Adds **GraphQL endpoint** using Strawberry
• enables flexible query language. | | [**Rate limiting**](https://github.com/darixsamani/fastapi-rate-limiter) | `from slowapi import Limiter`
`@limiter.limit("5/minute")`
`def endpoint():` | • **Throttles requests** per IP/user
• prevents API abuse. | | [**API versioning (URL)**](https://auth0.com/blog/fastapi-best-practices/) | `app.mount("/v1", v1_app)`
`app.mount("/v2", v2_app)` | • **Versions API via URL path**
• most common versioning strategy. | | [**API versioning (header)**](https://knowledgelib.io/software/patterns/api-versioning/2026) | `version = request.headers.get("API-Version", "v1")` | • Reads **version from custom header**
• cleaner URLs but less discoverable. | | [**Class-based views**](https://fastapi-utils.davidmontague.xyz/user-guide/class-based-views/) | `from fastapi_utils.cbv import cbv`
`@cbv(router)`
`class ItemAPI:`
` @router.get("/items")` | • Groups **related endpoints in class**
• reduces boilerplate for CRUD operations. | | [**MessagePack serialization**](https://mojoauth.com/serialize-and-deserialize/serialize-and-deserialize-messagepack-with-fastapi) | `from msgpack_asgi import MessagePackMiddleware`
`app.add_middleware(MessagePackMiddleware)` | • Uses **binary format** for smaller payloads
• faster than JSON for large data. | | [**Request ID tracking**](https://medium.com/@sizanmahmud08/securing-your-fastapi-application-with-middleware-a-production-ready-guide-part-2-8a6914f56e24) | `@app.middleware("http")`
`async def add_request_id(request, call_next):` | • Adds **unique ID to each request**
• enables distributed tracing. | ---

FastAPI Cheat Sheet

FastAPI Cheat Sheet

FastAPI Cheat Sheet

FastAPI Cheat Sheet