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:
from fastapi import HTTPException, WebSocketExceptionfastapi.HTTPException ¶
Section titled “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¶
Section titled “Example¶”from fastapi import FastAPI, HTTPException
app = FastAPI()
items = {"foo": "The Foo Wrestlers"}
@app.get("/items/{item_id}")
async def read_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: int |
detail |
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 TYPE: Any DEFAULT: None |
headers |
Any headers to send to the client in the response. Read more about it in the FastAPI docs for Handling Errors TYPE: Mapping[str, str] | None DEFAULT: None |
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](../tutorial/handling-errors.md#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](../tutorial/handling-errors.md#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](../tutorial/handling-errors.md#add-custom-headers)
"""
),
] = None,
) -> None:
super().__init__(status_code=status_code, detail=detail, headers=headers)status_code instance-attribute ¶
Section titled “status_code instance-attribute ¶”status_code = status_codedetail instance-attribute ¶
Section titled “detail instance-attribute ¶”detail = detailheaders instance-attribute ¶
Section titled “headers instance-attribute ¶”headers = headersfastapi.WebSocketException ¶
Section titled “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¶
Section titled “Example¶”from typing import Annotated
from fastapi import (
Cookie,
FastAPI,
WebSocket,
WebSocketException,
status,
)
app = FastAPI()
@app.websocket("/items/{item_id}/ws")
async def websocket_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: int |
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: str | None DEFAULT: None |
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)code instance-attribute ¶
Section titled “code instance-attribute ¶”code = codereason instance-attribute ¶
Section titled “reason instance-attribute ¶”reason = reason or ''