deprecating parameters

[Martin Pool]

On Sun, 2006-01-15 at 19:39 -0600, John Arbash Meinel wrote:
> Robert Collins wrote:
> > So, for symbol versioning in the branch-formats branch I needed to mark
> > Branch(..., init=XXX) as deprecated.
> > 
> > I've used the follow for now:
> > 
> >     def __init__(self, transport, init=deprecated_nonce,
> >                  relax_version_check=False):
> > ....
> > 
> >         if deprecated_passed(init):
> >             warn("BzrBranch.__init__(..., init=XXX): The init parameter
> > is "
> >                  "deprecated. Please use Branch.initialize().",
> >                  DeprecationWarning)
> > 
> > 
> > deprecated_nonce is a marker used by deprecated_passed - its assumed
> > noone will ever deliberately pass deprecated_none into a routine (and if
> > they do, their problem). (Its an object instance, theres no way to
> > accidentally do this).
> > 
> > 
> > I took this route because I was not sure how to make a -nice- parameter
> > deprecation decorator at this point - but I'm adding a TODO to research
> > that later.
> > 
> > Does this sound reasonable to folk ?
> > 
> > Rob
> > 
> 
> What do you consider to be a 'nice' parameter deprecation decorator.
> Because couldn't you do something like:
> 
> @deprecated_parameter(3, 'init')
> 
> And then inside the wrapper, you could check if 'args' is long enough to
> contain the deprecated parameter, or if 'kwargs' contains the keyword.
> 
> Nicer, probably would be to just do:
> @deprecated_parameter('init')

Or perhaps 

  def foo(@deprecated init)

but I don't know if you can even attach decorators to parameters. 

What Robert did looks quite reasonable to me.

I would perhaps call the magic value "DEPRECATED_PARAMETER" because:

 - it's sufficiently special that it deserves not to look like a regular
identifier (perhaps it should be DeprecatedParameter)

 - 'nonce' might be a bit strange for people who are not native english
speakers, and it's perhaps not used in the canonical technical sense of
a one-time random value, and it might be confused with None

-- 
Martin

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