tembo/dev/notes/custom_exceptions.md

Custom exceptions

Create an ./exceptions.py.

Define any custom exceptions. Can append Error to the exception name if needed, otherwise be descriptive.

E.g MismatchedTokenError, ScopedPageAlreadyExists.

(If it would raise a SystemExit(1) use an Error).

Can set custom attributes on the Exception:

class MismatchedTokenError(Exception):
    def __init__(self, expected: int, given: int) -> None:
        self.expected = expected
        self.given = given
        super().__init__()

Can refer to these when capturing the exception:

except exceptions.MismatchedTokenError as exec_info:
    click.echo(exec_info.expected, exec_info.given)
    # error handling

Alternatively you can pass arbitrary *args into the exceptions and capture them with args[0]:

raise exceptions.TemplateNotFoundError("some message")

except exceptions.TemplateFileNotFoundError as exec_info:
    cli_message(exec_info.args[0])