class LookupList(object):
    """
    A LookupList is a sequence whose elements can be named (and unlike
    a dictionary the order of the elements depends not on their key but
    on the order given by the user through construction) so that
    following syntactic constructions work as one would expect:
       example = Example(['x','y','z'],[1,2,3])
       example.x = [1, 2, 3] # set or change a field
       x, y, z = example
       x = example[0]
       x = example["x"]
       print example.keys() # returns ['x','y','z']
       print example.values() # returns [[1,2,3],2,3]
    """
    def __init__(self,names=[],values=[]):
        assert len(values)==len(names)
        self.__dict__['_values']=values
        self.__dict__['_name2index']={}
        self.__dict__['_names']=names
        for i in xrange(len(values)):
            self._name2index[names[i]]=i

    def keys(self):
        return self._names

    def values(self):
        return self._values

    def items(self):
        return zip(self._names,self._values)
    
    def __getitem__(self,key):
        """
        The key in example[key] can either be an integer to index the fields
        or the name of the field.
        """
        if isinstance(key,int):
            return self._values[key]
        else: # if not an int, key must be a name
            return self._values[self._name2index[key]]
    
    def __setitem__(self,key,value):
        if isinstance(key,int):
            self._values[key]=value
        else: # if not an int, key must be a name
            if key in self._name2index:
                self._values[self._name2index[key]]=value
            else:
                raise KeyError(key)

    def __getattr__(self,name):
        try:
            return self._values[self._name2index[name]]
        except KeyError, e:
            raise AttributeError(name)

    def append_keyval(self, key, value):
        self._name2index[key]=len(self)
        self._values.append(value)
        self._names.append(key)

    def __len__(self):
        return len(self._values)

    def __repr__(self):
        return "{%s}" % ", ".join([str(k) + "=" + repr(v) for k,v in self.items()])