Exceptions - HTTPException and WebSocketException¶
These are the exceptions that you can raise to show errors to the client.
When you raise an exception, as would happen with normal Python, the rest of the execution is aborted. This way you can raise these exceptions from anywhere in the code to abort a request and show the error to the client.
You can use:
HTTPExceptionWebSocketException
These exceptions can be imported directly from fastapi:
fromfastapiimport HTTPException, WebSocketException
fastapi.HTTPException ¶
HTTPException(status_code, detail=None, headers=None)
Bases: HTTPException
An HTTP exception you can raise in your own code to show errors to the client.
This is for client errors, invalid authentication, invalid data, etc. Not for server errors in your code.
Read more about it in the FastAPI docs for Handling Errors.
Example¶
fromfastapiimport FastAPI, HTTPException
app = FastAPI()
items = {"foo": "The Foo Wrestlers"}
@app.get("/items/{item_id}")
async defread_item(item_id: str):
if item_id not in items:
raise HTTPException(status_code=404, detail="Item not found")
return {"item": items[item_id]}
| PARAMETER | DESCRIPTION |
|---|---|
status_code
|
HTTP status code to send to the client. Read more about it in the FastAPI docs for Handling Errors
TYPE:
|
detail
|
Any data to be sent to the client in the Read more about it in the FastAPI docs for Handling Errors
TYPE:
|
headers
|
Any headers to send to the client in the response. Read more about it in the FastAPI docs for Handling Errors
TYPE:
|
Source code in fastapi/exceptions.py
def__init__(
self,
status_code: Annotated[
int,
Doc(
"""
HTTP status code to send to the client.
Read more about it in the
[FastAPI docs for Handling Errors](https://fastapi.tiangolo.com/tutorial/handling-errors/#use-httpexception)
"""
),
],
detail: Annotated[
Any,
Doc(
"""
Any data to be sent to the client in the `detail` key of the JSON
response.
Read more about it in the
[FastAPI docs for Handling Errors](https://fastapi.tiangolo.com/tutorial/handling-errors/#use-httpexception)
"""
),
] = None,
headers: Annotated[
Mapping[str, str] | None,
Doc(
"""
Any headers to send to the client in the response.
Read more about it in the
[FastAPI docs for Handling Errors](https://fastapi.tiangolo.com/tutorial/handling-errors/#add-custom-headers)
"""
),
] = None,
) -> None:
super().__init__(status_code=status_code, detail=detail, headers=headers)
fastapi.WebSocketException ¶
WebSocketException(code, reason=None)
Bases: WebSocketException
A WebSocket exception you can raise in your own code to show errors to the client.
This is for client errors, invalid authentication, invalid data, etc. Not for server errors in your code.
Read more about it in the FastAPI docs for WebSockets.
Example¶
fromtypingimport Annotated
fromfastapiimport (
Cookie,
FastAPI,
WebSocket,
WebSocketException,
status,
)
app = FastAPI()
@app.websocket("/items/{item_id}/ws")
async defwebsocket_endpoint(
*,
websocket: WebSocket,
session: Annotated[str | None, Cookie()] = None,
item_id: str,
):
if session is None:
raise WebSocketException(code=status.WS_1008_POLICY_VIOLATION)
await websocket.accept()
while True:
data = await websocket.receive_text()
await websocket.send_text(f"Session cookie is: {session}")
await websocket.send_text(f"Message text was: {data}, for item ID: {item_id}")
| PARAMETER | DESCRIPTION |
|---|---|
code
|
A closing code from the valid codes defined in the specification.
TYPE:
|
reason
|
The reason to close the WebSocket connection. It is UTF-8-encoded data. The interpretation of the reason is up to the application, it is not specified by the WebSocket specification. It could contain text that could be human-readable or interpretable by the client code, etc.
TYPE:
|
Source code in fastapi/exceptions.py
def__init__(
self,
code: Annotated[
int,
Doc(
"""
A closing code from the
[valid codes defined in the specification](https://datatracker.ietf.org/doc/html/rfc6455#section-7.4.1).
"""
),
],
reason: Annotated[
str | None,
Doc(
"""
The reason to close the WebSocket connection.
It is UTF-8-encoded data. The interpretation of the reason is up to the
application, it is not specified by the WebSocket specification.
It could contain text that could be human-readable or interpretable
by the client code, etc.
"""
),
] = None,
) -> None:
super().__init__(code=code, reason=reason)