Add fastapi example and remove black from dev dependencies (#69)

* Add fastapi example

* Remove black from dev dependencies

* Recent updates in Cargo.lock

* Add fluxqueue object declaration note in docs

Author: CCXLV

Cargo.lock

@@ -103,6 +103,13 @@ from fluxqueue import FluxQueue
 fluxqueue = FluxQueue()
 ```
 
+<!-- prettier-ignore -->
+!!! note
+    Creating a `FluxQueue` instance does **not** open a TCP connection to Redis.
+    The Redis connection is established only when a task is executed.
+    Because of this, declaring `fluxqueue` as a global object is safe and will not
+    create persistent or idle Redis connections.
+
 **`tasks/email.py`**:
 
 ```python

docs/tutorial/defininig_and_exposing_tasks.md

@@ -0,0 +1,13 @@
+# FluxQueue in FastAPI project
+
+This example shows how to use FluxQueue in a FastAPI project. In particular, it demonstrates an endpoint for sending emails asynchronously using `aiosmtplib`.
+
+You might wonder why we are declaring `fluxqueue` object globally.
+
+```py
+from fluxqueue import FluxQueue
+
+fluxqueue = FluxQueue()
+```
+
+This is safe because initializing the class does not establish a TCP connection to Redis. A connection is only created when a task function is actually executed.

examples/fastapi/README.md

@@ -0,0 +1,17 @@
+from contextlib import asynccontextmanager
+
+import aiosmtplib
+
+
+@asynccontextmanager
+async def get_email_client():
+    client = aiosmtplib.SMTP(
+        hostname="localhost",
+        port=2525,
+    )
+    try:
+        await client.connect()
+        yield client
+    finally:
+        if client.is_connected:
+            await client.quit()

examples/fastapi/src/__init__.py

@@ -0,0 +1,12 @@
+from fastapi import FastAPI
+
+from examples.fastapi.src.tasks import send_welcome_email_task
+
+app = FastAPI()
+
+
+@app.get("/email/{email}")
+async def send_welcome_email(email: str):
+    await send_welcome_email_task(email)
+
+    return {"message": "Email was sent"}

examples/fastapi/src/email/__init__.py

@@ -0,0 +1,3 @@
+__all__ = ["send_welcome_email_task"]
+
+from .email import send_welcome_email_task

examples/fastapi/src/email/core.py

@@ -0,0 +1,3 @@
+from fluxqueue import FluxQueue
+
+fluxqueue = FluxQueue()

examples/fastapi/src/main.py

@@ -0,0 +1,16 @@
+from email.message import EmailMessage
+
+from examples.fastapi.src.email.core import get_email_client
+from examples.fastapi.src.tasks.core import fluxqueue
+
+
+@fluxqueue.task()
+async def send_welcome_email_task(to_email: str):
+    async with get_email_client() as email_client:
+        message = EmailMessage()
+        message["From"] = "test@test.com"
+        message["To"] = to_email
+        message["Subject"] = "Welcome!"
+        message.set_content("Thanks for using FluxQueue")
+
+        await email_client.send_message(message)