📝 Add fist Dependency Injection docs

docs/tutorial/src/dependencies/tutorial003.py

@@ -0,0 +1,34 @@
+from typing import List
+
+from fastapi import Cookie, Depends, FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class InterestsTracker(BaseModel):
+    track_code: str
+    interests: List[str]
+
+
+fake_tracked_users_db = {
+    "Foo": {"track_code": "Foo", "interests": ["sports", "movies"]},
+    "Bar": {"track_code": "Bar", "interests": ["food", "shows"]},
+    "Baz": {"track_code": "Baz", "interests": ["gaming", "virtual reality"]},
+}
+
+
+async def get_tracked_interests(track_code: str = Cookie(None)):
+    if track_code in fake_tracked_users_db:
+        track_dict = fake_tracked_users_db[track_code]
+        track = InterestsTracker(**track_dict)
+        return track
+    return None
+
+
+@app.get("/interests/")
+async def read_interests(
+    tracked_interests: InterestsTracker = Depends(get_tracked_interests)
+):
+    response = {"interests": tracked_interests.interests}
+    return response