----- Original Message ----- From: "Raymond Hettinger" <python@rcn.com> To: <python-dev@python.org> Sent: Wednesday, June 26, 2002 3:45 PM Subject: Re: [Python-Dev] Dict constructor
From: "Tim Peters" <tim@zope.com>
-1 because of ambiguity. Is this trying to build a set with the single element (42, 666), or a mapping of 42 to 666?
dict([(42, 666)]}
I've been thinking about this and the unabiguous explicit solution is to specify a value argument like dict.get().
dict([(42, 666)]) # current behavior unchanged {42: 666}
dict([(42, 666)], True) {(42, 666): True}
dict( '0123456789abcdef', True) {'a': True, 'c': True, 'b': True, 'e': True, 'd': True, 'f': True, '1': True, '0': True, '3': True, '2': True, '5': True, '4': True, 7': True, '6': True, '9': True, '8': True}
dict('0123456789abcdef') # current behavior unchanged ValueError: dictionary update sequence element #0 has length 1; 2 is required
The goal is not to provide full set behavior but to facilitate the common task of building dictionaries with a constant value. It comes up in membership testing and in uniquifying sequences. The task of dict() is to construct dictionaries and this is a reasonably common construction.
But is it really common enough to merit special-casing what can anyway be spelt very simply: adict = {} for k in asequence: dict[k] = sentinel ? regards ----------------------------------------------------------------------- Steve Holden http://www.holdenweb.com/ Python Web Programming http://pydish.holdenweb.com/pwp/ -----------------------------------------------------------------------