Breaking Changes
Dependencies with yield can now catch HTTPException and custom exceptions. For example:
async def get_database():
with Session() as session:
try:
yield session
except HTTPException:
session.rollback()
raise
finally:
session.close()After the dependency with yield handles the exception (or not) the exception is raised again. So that any exception handlers can catch it, or ultimately the default internal ServerErrorMiddleware.
If you depended on exceptions not being received by dependencies with yield, and receiving an exception breaks the code after yield, you can use a block with try and finally:
async def do_something():
try:
yield something
finally:
some_cleanup()...that way the finally block is run regardless of any exception that might happen.
Features
- The same PR #4575 from above also fixes the
contextvarscontext for the code before and afteryield. This was the main objective of that PR.
This means that now, if you set a value in a context variable before yield, the value would still be available after yield (as you would intuitively expect). And it also means that you can reset the context variable with a token afterwards.
For example, this works correctly now:
from contextvars import ContextVar
from typing import Any, Dict, Optional
legacy_request_state_context_var: ContextVar[Optional[Dict[str, Any]]] = ContextVar(
"legacy_request_state_context_var", default=None
)
async def set_up_request_state_dependency():
request_state = {"user": "deadpond"}
contextvar_token = legacy_request_state_context_var.set(request_state)
yield request_state
legacy_request_state_context_var.reset(contextvar_token)...before this change it would raise an error when resetting the context variable, because the contextvars context was different, because of the way it was implemented.
Note: You probably don't need contextvars, and you should probably avoid using them. But they are powerful and useful in some advanced scenarios, for example, migrating from code that used Flask's g semi-global variable.
Technical Details: If you want to know more of the technical details you can check out the PR description #4575.