[Python-Dev] Re: PEP309 re-written (original) (raw)

Peter Harris scav at blueyonder.co.uk
Mon Apr 5 19:29:10 EDT 2004

David Abrams wrote:

_C = lambda *args, **kw: _ Canvas(mywindow, width=100, height=100, bg='white', *args, **kw) C(bg='red')

Traceback (most recent call last): File "<pyshell#4>", line 1, in -toplevel- C(bg='red') File "<pyshell#3>", line 1, in C = lambda *args, **kw:
TypeError: Canvas constructor got multiple values for keyword argument 'bg'

OK, partial is a little shorter in that case. I'm not sure that example justifies a PEP, though.

PEPs can be for the little things too.

def merge(d1, d2): d1.update(d2) return d1

def partial(f, *args, **kw): return lambda *args2, **kw2: f(args + args2, merge(kw2,kw)) ?? def partial(f, *args, **kw): def _merge(d1, d2): d1.update(d2) return d1 return lambda *args2, *kw2: f((args + args2), **_merge(kw2,kw))

A good implementation indeed. I may be inclined to provide both a class called Partial (for people who want to mess with the internals, or for some other reason want a class) and a function called partial.

Would that be OK, everyone?

You could maybe sub-class partial to override call , in case you want to do anything fancy like pre-supplying arguments at arbitrary positions.

A perfect example of what lambda is already good at. Yup, no argument from me there. I can't foresee what others may one day want to do, however.

Peter Harris

More information about the Python-Dev mailing list