[Tutor] Why doesn't this work?

[Jason Massey]

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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