🔗 ⏮️ 🌾

FastAPI 🐕‍🦺 🔗 👈 ➕ 🔁 ⏮️ 🏁.

👉, ⚙️ yield ↩️ return, & ✍ ➕ 🔁 ⏮️.

Tip

⚒ 💭 ⚙️ yield 1️⃣ 👁 🕰.

📡 ℹ

🙆 🔢 👈 ☑ ⚙️ ⏮️:

• @contextlib.contextmanager ⚖️
• @contextlib.asynccontextmanager

🔜 ☑ ⚙️ FastAPI 🔗.

👐, FastAPI ⚙️ 📚 2️⃣ 👨‍🎨 🔘.

💽 🔗 ⏮️ yield

🖼, 👆 💪 ⚙️ 👉 ✍ 💽 🎉 & 🔐 ⚫️ ⏮️ 🏁.

🕴 📟 ⏭ & 🔌 yield 📄 🛠️ ⏭ 📨 📨:

Python 3.8+

async def get_db():
    db = DBSession()
    try:
        yield db
    finally:
        db.close()

🌾 💲 ⚫️❔ 💉 🔘 ➡ 🛠️ & 🎏 🔗:

Python 3.8+

async def get_db():
    db = DBSession()
    try:
        yield db
    finally:
        db.close()

📟 📄 yield 📄 🛠️ ⏮️ 📨 ✔️ 🚚:

Python 3.8+

async def get_db():
    db = DBSession()
    try:
        yield db
    finally:
        db.close()

Tip

👆 💪 ⚙️ async ⚖️ 😐 🔢.

FastAPI 🔜 ▶️️ 👜 ⏮️ 🔠, 🎏 ⏮️ 😐 🔗.

🔗 ⏮️ yield & try

🚥 👆 ⚙️ try 🍫 🔗 ⏮️ yield, 👆 🔜 📨 🙆 ⚠ 👈 🚮 🕐❔ ⚙️ 🔗.

🖼, 🚥 📟 ☝ 🖕, ➕1️⃣ 🔗 ⚖️ ➡ 🛠️, ⚒ 💽 💵 "💾" ⚖️ ✍ 🙆 🎏 ❌, 👆 🔜 📨 ⚠ 👆 🔗.

, 👆 💪 👀 👈 🎯 ⚠ 🔘 🔗 ⏮️ except SomeException.

🎏 🌌, 👆 💪 ⚙️ finally ⚒ 💭 🚪 📶 🛠️, 🙅‍♂ 🤔 🚥 📤 ⚠ ⚖️ 🚫.

Python 3.8+

async def get_db():
    db = DBSession()
    try:
        yield db
    finally:
        db.close()

🎧-🔗 ⏮️ yield

👆 💪 ✔️ 🎧-🔗 & "🌲" 🎧-🔗 🙆 📐 & 💠, & 🙆 ⚖️ 🌐 👫 💪 ⚙️ yield.

FastAPI 🔜 ⚒ 💭 👈 "🚪 📟" 🔠 🔗 ⏮️ yield 🏃 ☑ ✔.

🖼, dependency_c 💪 ✔️ 🔗 🔛 dependency_b, & dependency_b 🔛 dependency_a:

Python 3.8+ - non-Annotated

from fastapi import Depends


async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a=Depends(dependency_a)):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)


async def dependency_c(dep_b=Depends(dependency_b)):
    dep_c = generate_dep_c()
    try:
        yield dep_c
    finally:
        dep_c.close(dep_b)

🤓 Other versions and variants

Python 3.9+Python 3.8+

from typing import Annotated

from fastapi import Depends


async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a: Annotated[DepA, Depends(dependency_a)]):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)


async def dependency_c(dep_b: Annotated[DepB, Depends(dependency_b)]):
    dep_c = generate_dep_c()
    try:
        yield dep_c
    finally:
        dep_c.close(dep_b)

from fastapi import Depends
from typing_extensions import Annotated


async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a: Annotated[DepA, Depends(dependency_a)]):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)


async def dependency_c(dep_b: Annotated[DepB, Depends(dependency_b)]):
    dep_c = generate_dep_c()
    try:
        yield dep_c
    finally:
        dep_c.close(dep_b)

& 🌐 👫 💪 ⚙️ yield.

👉 💼 dependency_c, 🛠️ 🚮 🚪 📟, 💪 💲 ⚪️➡️ dependency_b (📥 📛 dep_b) 💪.

& , 🔄, dependency_b 💪 💲 ⚪️➡️ dependency_a (📥 📛 dep_a) 💪 🚮 🚪 📟.

Python 3.8+ - non-Annotated

from fastapi import Depends


async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a=Depends(dependency_a)):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)


async def dependency_c(dep_b=Depends(dependency_b)):
    dep_c = generate_dep_c()
    try:
        yield dep_c
    finally:
        dep_c.close(dep_b)

🤓 Other versions and variants

Python 3.9+Python 3.8+

from typing import Annotated

from fastapi import Depends


async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a: Annotated[DepA, Depends(dependency_a)]):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)


async def dependency_c(dep_b: Annotated[DepB, Depends(dependency_b)]):
    dep_c = generate_dep_c()
    try:
        yield dep_c
    finally:
        dep_c.close(dep_b)

from fastapi import Depends
from typing_extensions import Annotated


async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a: Annotated[DepA, Depends(dependency_a)]):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)


async def dependency_c(dep_b: Annotated[DepB, Depends(dependency_b)]):
    dep_c = generate_dep_c()
    try:
        yield dep_c
    finally:
        dep_c.close(dep_b)

🎏 🌌, 👆 💪 ✔️ 🔗 ⏮️ yield & return 🌀.

& 👆 💪 ✔️ 👁 🔗 👈 🚚 📚 🎏 🔗 ⏮️ yield, ♒️.

👆 💪 ✔️ 🙆 🌀 🔗 👈 👆 💚.

FastAPI 🔜 ⚒ 💭 🌐 🏃 ☑ ✔.

📡 ℹ

👉 👷 👏 🐍 🔑 👨‍💼.

FastAPI ⚙️ 👫 🔘 🏆 👉.

🔗 ⏮️ yield & HTTPException

👆 👀 👈 👆 💪 ⚙️ 🔗 ⏮️ yield & ✔️ try 🍫 👈 ✊ ⚠.

⚫️ 5️⃣📆 😋 🤚 HTTPException ⚖️ 🎏 🚪 📟, ⏮️ yield. ✋️ ⚫️ 🏆 🚫 👷.

🚪 📟 🔗 ⏮️ yield 🛠️ ⏮️ 📨 📨, ⚠ 🐕‍🦺 🔜 ✔️ ⏪ 🏃. 📤 🕳 😽 ⚠ 🚮 👆 🔗 🚪 📟 (⏮️ yield).

, 🚥 👆 🤚 HTTPException ⏮️ yield, 🔢 (⚖️ 🙆 🛃) ⚠ 🐕‍🦺 👈 ✊ HTTPExceptionⓂ & 📨 🇺🇸🔍 4️⃣0️⃣0️⃣ 📨 🏆 🚫 📤 ✊ 👈 ⚠ 🚫🔜.

👉 ⚫️❔ ✔ 🕳 ⚒ 🔗 (✅ 💽 🎉), 🖼, ⚙️ 🖥 📋.

🖥 📋 🏃 ⏮️ 📨 ✔️ 📨. 📤 🙅‍♂ 🌌 🤚 HTTPException ↩️ 📤 🚫 🌌 🔀 📨 👈 ⏪ 📨.

✋️ 🚥 🖥 📋 ✍ 💽 ❌, 🌘 👆 💪 💾 ⚖️ 😬 🔐 🎉 🔗 ⏮️ yield, & 🎲 🕹 ❌ ⚖️ 📄 ⚫️ 🛰 🕵 ⚙️.

🚥 👆 ✔️ 📟 👈 👆 💭 💪 🤚 ⚠, 🏆 😐/"🙃" 👜 & 🚮 try 🍫 👈 📄 📟.

🚥 👆 ✔️ 🛃 ⚠ 👈 👆 🔜 💖 🍵 ⏭ 🛬 📨 & 🎲 ❎ 📨, 🎲 🙋‍♀ HTTPException, ✍ 🛃 ⚠ 🐕‍🦺.

Tip

👆 💪 🤚 ⚠ 🔌 HTTPException ⏭ yield. ✋️ 🚫 ⏮️.

🔁 🛠️ 🌅 ⚖️ 🌘 💖 👉 📊. 🕰 💧 ⚪️➡️ 🔝 🔝. & 🔠 🏓 1️⃣ 🍕 🔗 ⚖️ 🛠️ 📟.

sequenceDiagram

participant client as Client
participant handler as Exception handler
participant dep as Dep with yield
participant operation as Path Operation
participant tasks as Background tasks

    Note over client,tasks: Can raise exception for dependency, handled after response is sent
    Note over client,operation: Can raise HTTPException and can change the response
    client ->> dep: Start request
    Note over dep: Run code up to yield
    opt raise
        dep -->> handler: Raise HTTPException
        handler -->> client: HTTP error response
        dep -->> dep: Raise other exception
    end
    dep ->> operation: Run dependency, e.g. DB session
    opt raise
        operation -->> dep: Raise HTTPException
        dep -->> handler: Auto forward exception
        handler -->> client: HTTP error response
        operation -->> dep: Raise other exception
        dep -->> handler: Auto forward exception
    end
    operation ->> client: Return response to client
    Note over client,operation: Response is already sent, can't change it anymore
    opt Tasks
        operation -->> tasks: Send background tasks
    end
    opt Raise other exception
        tasks -->> dep: Raise other exception
    end
    Note over dep: After yield
    opt Handle other exception
        dep -->> dep: Handle exception, can't change response. E.g. close DB session.
    end

Info

🕴 1️⃣ 📨 🔜 📨 👩‍💻. ⚫️ 💪 1️⃣ ❌ 📨 ⚖️ ⚫️ 🔜 📨 ⚪️➡️ ➡ 🛠️.

⏮️ 1️⃣ 📚 📨 📨, 🙅‍♂ 🎏 📨 💪 📨.

Tip

👉 📊 🎦 HTTPException, ✋️ 👆 💪 🤚 🙆 🎏 ⚠ ❔ 👆 ✍ 🛃 ⚠ 🐕‍🦺.

🚥 👆 🤚 🙆 ⚠, ⚫️ 🔜 🚶‍♀️ 🔗 ⏮️ 🌾, 🔌 HTTPException, & ⤴️ 🔄 ⚠ 🐕‍🦺. 🚥 📤 🙅‍♂ ⚠ 🐕‍🦺 👈 ⚠, ⚫️ 🔜 ⤴️ 🍵 🔢 🔗 ServerErrorMiddleware, 🛬 5️⃣0️⃣0️⃣ 🇺🇸🔍 👔 📟, ➡️ 👩‍💻 💭 👈 📤 ❌ 💽.

🔑 👨‍💼

⚫️❔ "🔑 👨‍💼"

"🔑 👨‍💼" 🙆 👈 🐍 🎚 👈 👆 💪 ⚙️ with 📄.

🖼, 👆 💪 ⚙️ with ✍ 📁:

with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)

🔘, open("./somefile.txt") ✍ 🎚 👈 🤙 "🔑 👨‍💼".

🕐❔ with 🍫 🏁, ⚫️ ⚒ 💭 🔐 📁, 🚥 📤 ⚠.

🕐❔ 👆 ✍ 🔗 ⏮️ yield, FastAPI 🔜 🔘 🗜 ⚫️ 🔑 👨‍💼, & 🌀 ⚫️ ⏮️ 🎏 🔗 🧰.

⚙️ 🔑 👨‍💼 🔗 ⏮️ yield

Warning

👉, 🌅 ⚖️ 🌘, "🏧" 💭.

🚥 👆 ▶️ ⏮️ FastAPI 👆 💪 💚 🚶 ⚫️ 🔜.

🐍, 👆 💪 ✍ 🔑 👨‍💼 🏗 🎓 ⏮️ 2️⃣ 👩‍🔬: __enter__() & __exit__().

👆 💪 ⚙️ 👫 🔘 FastAPI 🔗 ⏮️ yield ⚙️ with ⚖️ async with 📄 🔘 🔗 🔢:

Python 3.8+

class MySuperContextManager:
    def __init__(self):
        self.db = DBSession()

    def __enter__(self):
        return self.db

    def __exit__(self, exc_type, exc_value, traceback):
        self.db.close()


async def get_db():
    with MySuperContextManager() as db:
        yield db

Tip

➕1️⃣ 🌌 ✍ 🔑 👨‍💼 ⏮️:

• @contextlib.contextmanager ⚖️
• @contextlib.asynccontextmanager

⚙️ 👫 🎀 🔢 ⏮️ 👁 yield.

👈 ⚫️❔ FastAPI ⚙️ 🔘 🔗 ⏮️ yield.

✋️ 👆 🚫 ✔️ ⚙️ 👨‍🎨 FastAPI 🔗 (& 👆 🚫🔜 🚫).

FastAPI 🔜 ⚫️ 👆 🔘.