PEP 327: Decimal Data Type

[Josiah Carlson]

> But if you normalise every time, some theoretically simple operations
> can become relatively very expensive in terms of time. (Basically,
> things like addition, which suddenly require a GCD calculation).

If we are to take cues from standard Python numeric types, any 
mathematical calculation results in a new immutable object.  Thusly, 
only normalizing on initialization is sufficient.  Since that is the 
only time you ever get anything new, doing GCD on initialization is the 
minimum and maximum requirement.

  - Josiah