[pypy-dev] gateway.applevel and kwargs

Armin Rigo arigo at tunes.org
Tue Aug 1 13:41:59 CEST 2006

Hi Leonardo,

On Sat, Jul 29, 2006 at 09:11:14PM -0400, Leonardo Soto wrote:
> I've recently filled the issue 244 (dict.update() doesn't support
> keywords argument), and tried to solve it in a naive way, just
> modifying the applevel  definition to:
>     def update(d, o, **kwargs):
>         (...)

This is a bit messy.  It's an app-level definition but it goes through
the interp-level gateway code via the multimethod logic.  The first
thing to change is the declared signature of the dict_update
multimethod, also in dicttype.py:

    dict_update = SMM('update', 2, defaults=((),), doc="...")

This means "two arguments with a default of () for the second one".
Note that it's where the default comes from, too; not from the
"def update(d, o)" implementation.

Note first a difficulty: if we were implementing this method in pure
Python, we couldn't say  'def update(self, o, **kwargs)'  because there is
a name clash between 'o' and the keywords, preventing an explicit 'o'
keyword from being passed.  To solve this we would have to declare it
'def update(self, *args, **kwargs)'.

The equivalent solution here is:

    dict_update = SMM('update', 1, general__args__=True, doc="...")

    def update(d, *args, **kwargs):
        if len(args) > 1:
            raise TypeError("update takes at most 1 (non-keyword) argument")

    dict_update__ANY = app.interphook("update")

But it doesn't work yet, because I'm just discovering that we have no
support for *args/**kwargs in app.interphook()!

Trying to fix this now...


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