In article
<039360fb-a29c-4f43-b6e0-ba97fb598...@z23g2000prd.googlegroups.com>,
Mensanator <mensana...@aol.com> wrote:
> On Mar 26, 11:42 am, "andrew cooke" <and...@acooke.org> wrote:
> > David C. Ullrich wrote:
> > > In article <mailman.2701.1238060157.11746.python-l...@python.org>,
> > > "Paddy O'Loughlin" <patrick.olough...@gmail.com> wrote:
> >
> > > Here's my favorite thing about Python (you'd of course
> > > remark that it's just a toy example, doing everything
> > > in as dumb but easily understood way as possible):
> >
> > > x=[1,2]
> >
> > > print x+x
> >
> > > class Vector():
> > > def __init__(self, data):
> > > self.data = data
> > > def __repr__(self):
> > > return repr(self.data)
> > > def __add__(self, other):
> > > return Vector([self.data[0]+other.data[0],
> > > self.data[1]+other.data[1]])
> >
> > > x = Vector([1,2])
> >
> > > print x+x
> >
> > that's cute, but if you show them 2.6 or 3 it's even cuter:
> >
> > >>> from operator import add
> > >>> class Vector(list):
> >
> > ... def __add__(self, other):
> > ... return map(add, self, other)
> > ...>>> x = Vector([1,2])
> > >>> x+x
> >
> > [2, 4]
> >
> > andrew
>
> Mind if I ask a question? In DU's code, both operands have to
> be instances of the Vector class?
Yes, in the code I posted. That code was not meant to be
an example of the right way to do anything, just an
illustration of how wonderful things like __add__ can be.
> >>> x = Vector([1,2])
> >>> x+x
> [2, 4]
> >>> x+[3,3]
>
> Traceback (most recent call last):
> File "<pyshell#60>", line 1, in <module>
> x+[3,3]
> File "<pyshell#55>", line 7, in __add__
> return SV([self.data[0]+other.data[0],self.data[1]+other.data[1]])
> AttributeError: 'list' object has no attribute 'data'
>
>
> Whereas with your version, "other" just has to be an iterable.
>
> >>> x = Vector([1,2])
> >>> x+x
> [2, 4]
> >>> x+[3,3]
> [4, 5]
> >>> x+(9,9)
> [10, 11]
> >>> x+{3:4,4:9}
> [4, 6]
>
> Although it does require the same number of elements (because that's
> required by map and could be changed if necessary).
>
> >>> x+[3,3,3]
>
> Traceback (most recent call last):
> File "<pyshell#71>", line 1, in <module>
> x+[3,3,3]
> File "<pyshell#62>", line 3, in __add__
> return map(add,self,other)
> TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'
>
>
> What would you have to do to make this work?
>
> >>> x+x+x # expecting [3,6]
> [2, 4, 1, 2]
--
David C. Ullrich
--
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