duplicity.errors.ConflictingScheme:
Raised to indicate an attempt was made to register a backend for a
scheme for which there is already a backend registered.
duplicity.errors.NotSupported:
Exception raised when an action cannot be completed because some
particular feature is not supported by the environment.
duplicity.errors.UserError:
Subclasses use this in their inheritance hierarchy to signal that
the error is a user generated one, and that it is therefore
typically unsuitable to display a full stack trace.