subclass list

[Mark McEahern]

Suppose I want to subclass list so that my subclass has optionally unique
values.  I'm using Python 2.2, so I start out like this:

class Bucket(list):

	def __init__(self, unique):
		self.unique = unique
		# Use a dict to keep track of unique values.
		if self.unique:
			self.keys = {}

Q:  How do I override append() so that I can determine whether to add the
value or not?

I tried:

    def append(self, value):
        if not self.unique or (self.unique and not
self.keys.has_key(value)):
            list.append(value)
            if self.unique:
                self.keys[value] = None

But then I get:

Traceback (most recent call last):
  File "./junk.py", line 31, in ?
    print getRandom(count=10)
  File "./junk.py", line 29, in getRandom
    bucket.append(random.randint(low, hi))
  File "./junk.py", line 22, in append
    list.append(value)
TypeError: descriptor 'append' requires a 'list' object but received a 'int'

Thanks,

// mark