[Tutor] Why doesn't this work?

[Christopher Spears]

Thanks!  Is there a name for the type of myopia that
develops after staring at the computer screen too
long?

-Chris

--- Jason Massey <jason.massey at gmail.com> wrote:

> Christopher,
> 
> I copied and pasted your code and it worked only a
> few modifications.  The
> thing I had to change was the indention level of
> the:
> 
> def __and__(self, other): return
> self.intersect(other)
> def __or__(self, other): return self.union(other)
> def __repr__(self): return 'Set:' +
> list.__repr__(self)
> 
> statements.  These statements need to be on the same
> indention level as your
> __init__, intersection and union satements.
> 
> Here's what I got:
> 
> class Set(list):
>     def __init__(self, value=[]):
>         list.__init__([])
>         self.concat(value)
> 
>     def intersect(self, other):
>         res = []
>         for x in self:
>             if x in other:
>                 res.append(x)
>         return Set(res)
> 
>     def union(self, other):
>         res = Set(self)
>         res.concat(other)
>         return res
> 
>     def concat(self, value):
>         for x in value:
>             if not x in self:
>                 self.append(x)
> 
>     def __and__(self, other): return
> self.intersect(other)
>     def __or__(self, other): return
> self.union(other)
>     def __repr__(self): return 'Set:' +   
> list.__repr__(self)
> 
> if __name__ == '__main__':
>     x = Set([1,3,5,7])
>     y = Set([2,1,4,5,6])
>     print x, y, len(x)
>     print x.intersect(y), y.union(x)
>     print x & y, x | y
>     x.reverse();
>     print x
> 
> On 1/23/06, Christopher Spears
> <cspears2002 at yahoo.com> wrote:
> >
> > I copied this code from Learning Python while
> learning
> > about extending types by subclassing:
> >
> > class Set(list):
> >         def __init__(self, value=[]):
> >                 list.__init__([])
> >                 self.concat(value)
> >
> >         def intersect(self, other):
> >                 res = []
> >                 for x in self:
> >                         if x in other:
> >                                 res.append(x)
> >                 return Set(res)
> >
> >         def union(self, other):
> >                 res = Set(self)
> >                 res.concat(other)
> >                 return res
> >
> >         def concat(self, value):
> >                 for x in value:
> >                         if not x in self:
> >                                 self.append(x)
> >
> > def __and__(self, other): return
> self.intersect(other)
> > def __or__(self, other): return self.union(other)
> > def __repr__(self): return 'Set:' +
> > list.__repr__(self)
> >
> > if __name__ == '__main__':
> >         x = Set([1,3,5,7])
> >         y = Set([2,1,4,5,6])
> >         print x, y, len(x)
> >         print x.intersect(y), y.union(x)
> >         print x & y, x | y
> >         x.reverse(); print x
> >
> > Here is the result:
> >
> >
>
cspears at iaws09:/imports/home/cspears/Documents/Python/chap23>
> > python setsubclass.py
> > [1, 3, 5, 7] [2, 1, 4, 5, 6] 4
> > [1, 5] [2, 1, 4, 5, 6, 3, 7]
> > Traceback (most recent call last):
> >   File "setsubclass.py", line 32, in ?
> >     print x & y, x | y
> > TypeError: unsupported operand type(s) for &:
> 'Set'
> > and 'Set'
> >
> > According to the book, here is what I should get:
> >
> > Set:[1, 3, 5, 7] Set:[2, 1, 4, 5, 6] 4
> > Set:[1, 5] Set:[2, 1, 4, 5, 6, 3, 7]
> > Set:[1, 5] Set:[1, 3, 5, 7, 2, 4, 6]
> > Set:[7, 5, 3, 1]
> >
> > Problem 1:  Why isn't "Set:" being printed?  I
> thought
> >
> >
> >    def __repr__(self): return 'Set:' +
> > list.__repr__(self)
> >
> > would facilitate that.
> >
> > Problem 2: What is causing the TypeError?
> >
> > I'm pretty sure I copied this exactly from the
> book,
> > so I'm not sure what is not working.
> > _______________________________________________
> > Tutor maillist  -  Tutor at python.org
> > http://mail.python.org/mailman/listinfo/tutor
> >
> 


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