[Python-Dev] decimal.Context.copy() shallow or deep?

[Tim Peters]

[Raymond Hettinger]
> Currently, the copy() method for Context objects makes a shallow copy of
> the context.  To get a deepcopy, you have to use
> copy.deepcopy(thecontext).
>
> Though, copies are usually shallow and deepcopies are deep, I'm now
> having misgivings about the copy method.  I would think that a deep copy
> is almost invariably what you would want and expect, (i.e. the copy
> doesn't share traps and flags with the original).

Hmm.  In my head (which I'm sure doesn't match reality, else you
wouldn't be saying this), sets of trap-enabled and it-happened sticky
flags are just integers with meanings assigned to the bits, as they
are in hardware and most APIs for controlling and querying FPU status.
 Then there's no difference between shallow and deep copying.

> Do you guys think it should be left alone (shallow) or changed (made
> deep)?

A user-visible copy certainly should not share mutable state with the
original.  It's possible that really argues for a simpler internal
representation of such state, though.

> The wrinkle in all this is that internally the module makes many uses of
> copy and expects it to be shallow (or least, tests fail in droves when
> copy is made deep).  So I would have to rename the current copy to
> _shallow_copy and replace the original with a deep version for the
> public API.
>
> Any thoughts?

Whatever works <wink>.