[Python-Dev] Updated PEP 362 (Function Signature Object) (original) (raw)

R. David Murray rdmurray at bitdance.com
Thu Jun 7 16:45:34 CEST 2012

On Thu, 07 Jun 2012 07:00:29 -0700, Larry Hastings <larry at hastings.org> wrote:

On 06/06/2012 11:56 PM, Nick Coghlan wrote: > I'd say return a copy in the first case to be safe against accidental > modification. If someone actually wants in-place modification, they > can access signature directly.

I really don't understand this anxiety about mutable Signature objects. Can you give a plausible example of "accidental modification" of a Signature object? I for one--as clumsy as I am--cannot recall ever "accidentally" modifying an object.

Maybe it would make more sense if you read that as "naively" rather than "accidentally"?

In the 3.3 email extension I made a similar decision, although there I went even further and made the objects read only. My logic for doing this is that a naive user would...naively...try to set the attributes and expect the object they got it from to change, but that object (a string subclass) is inherently read-only.

I am thinking that in fact we may ultimately want to return copies of these objects that are mutable, because that might be useful, but I'm starting with read-only because it is easy to make them mutable later but pretty much impossible (backward compatibility wise) to make them immutable if they start mutable.

I see the signature object as a very parallel case to this, except that it is already obvious that having them be a mutable copy is useful.

--David

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