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Error Handling#

Errors are a natural part of code, and thus, of commands too. arc offers you the ability to handle errors in a nice and ergonomic manner, with automatic error propagation if an error handler fails.

Error Handlers#

To register a local error handler on a command, group, plugin, or the client, use the @set_error_handler decorator method. A function can be used as an error handler if it takes a Context and an Exception as it's sole parameters, returns None. Error handler functions must also be async.

@client.include
@arc.slash_command("name", "description")
async def error_command_func(ctx: arc.GatewayContext) -> None:
    raise RuntimeError("I'm an error!")

# 'error_command_func' in this case is the command function name
@error_command_func.set_error_handler
async def error_handler(ctx: arc.GatewayContext, exc: Exception) -> None:
    if isinstance(exc, RuntimeError):
        print(f"Handled error: {exc}")
        return
    raise exc

@client.include
@arc.slash_command("name", "description")
async def error_command_func(ctx: arc.RESTContext) -> None:
    raise RuntimeError("I'm an error!")

# 'error_command_func' in this case is the command function name
@error_command_func.set_error_handler
async def error_handler(ctx: arc.RESTContext, exc: Exception) -> None:
    if isinstance(exc, RuntimeError):
        print(f"Handled error: {exc}")
        return
    raise exc

Warning

Errors that the current error handler cannot handle must be re-raised, otherwise the error will be silently ignored. This is true of the global error handler (the one added to the client) as well, otherwise tracebacks will not be printed to the console.

This can also be used as a regular function if using a decorator is not feasible:

@arc.loader
async def load(client: arc.GatewayClient) -> None:
    client.set_error_handler(some_func)

@arc.loader
async def load(client: arc.RESTClient) -> None:
    client.set_error_handler(some_func)

Error handler resolution order#

  • Command
  • Command Group (if any)
  • Plugin (if any)
  • Client

If none of the error handlers handle an exception, it will be, by default, printed to the console with a full traceback.