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:
[EMAIL PROTECTED]:/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.
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