[Python] How is passing a generator to Depends make the generator act like a contextmanager?

I was going through a tutorial on fast api and I came across something like below

def get_db():
try:
db = SessionLocal()
yield db
finally:
print("from finally block")
db.close()


@app.get("/")
async def read_all(db: Session = Depends(get_db)):
res = db.query(models.Todos).all()
print("from endpoint")
return res


result

INFO: 127.0.0.1:39088 - "GET /openapi.json HTTP/1.1" 200 OK
from endpoint
INFO: 127.0.0.1:39088 - "GET / HTTP/1.1" 200 OK
from finally block



why does Depends(get_db) seem to act like somekind of contextmanager?. the "from finally block" print statement does not get executed until the end of the read_all method

doing something like


class SomeDependency:
def __enter__(self):
print("entering")
def __exit__(self, exc_type, exc_val, exc_tb):
print("exited")

def hello():
try:
yield SomeDependency()
finally:
print("yolo")

if __name__ == "__main__":
next(hello())


the finally block gets executed immediately after the call to next.

what why does the finally block of the get_db not execute immediately when passed to Depends?

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