python list/dict 属性最佳实践

Question

我有一个类对象，它存储一些属性，这些属性是其他对象的列表。列表中的每个项目都有一个标识符，可以使用 id 属性访问该标识符。我希望能够从这些列表中读取和写入，但也能够访问由其标识符键入的字典。让我用一个例子来说明:

class Child(object):
    def __init__(self, id, name):
        self.id = id
        self.name = name

class Teacher(object):
    def __init__(self, id, name):
        self.id = id
        self.name = name

class Classroom(object):
    def __init__(self, children, teachers):
        self.children = children
        self.teachers = teachers

classroom = Classroom([Child('389','pete')],
                      [Teacher('829','bob')])

这是一个愚蠢的例子，但它说明了我正在尝试做的事情。我希望能够像这样与教室对象进行交互:

#access like a list
print classroom.children[0]
#append like it's a list
classroom.children.append(Child('2344','joe'))
#delete from like it's a list
classroom.children.pop(0)

但我也希望能够像访问字典一样访问它，并且当我修改列表时字典应该自动更新:

#access like a dict
print classroom.childrenById['389']

我知道我可以把它变成一个字典，但我想避免这样的代码:

classroom.childrendict[child.id] = child

我也可能有几个这样的属性，所以我不想添加像 addChild 这样的函数，反正感觉很不符合 Python 风格。有没有办法以某种方式对 dict 和/或 list 进行子类化，并使用我的类的属性轻松提供所有这些功能？我还想尽可能避免使用代码。

Answer 1

索引列表类:

class IndexedList(list):
    def __init__(self, items, attrs):
        super(IndexedList,self).__init__(items)
        # do indexing
        self._attrs = tuple(attrs)
        self._index = {}
        _add = self._addindex
        for obj in self:
            _add(obj)

    def _addindex(self, obj):
        _idx = self._index
        for attr in self._attrs:
            _idx[getattr(obj, attr)] = obj

    def _delindex(self, obj):
        _idx = self._index
        for attr in self._attrs:
            try:
                del _idx[getattr(obj,attr)]
            except KeyError:
                pass

    def __delitem__(self, ind):
        try:
            obj = list.__getitem__(self, ind)
        except (IndexError, TypeError):
            obj = self._index[ind]
            ind = list.index(self, obj)
        self._delindex(obj)
        return list.__delitem__(self, ind)

    def __delslice__(self, i, j):
        for ind in xrange(i,j):
            self.__delitem__(ind)

    def __getitem__(self, ind):
        try:
            return self._index[ind]
        except KeyError:
            return list.__getitem__(self, ind)

    def __getslice__(self, i, j):            
        return IndexedList(list.__getslice__(self, i, j))

    def __setitem__(self, ind, new_obj):
        try:
            obj = list.__getitem__(self, ind)
        except (IndexError, TypeError):
            obj = self._index[ind]
            ind = list.index(self, obj)
        self._delindex(obj)
        self._addindex(new_obj)
        return list.__setitem__(ind, new_obj)

    def __setslice__(self, i, j, newItems):
        _get = self.__getitem__
        _add = self._addindex
        _del = self._delindex
        newItems = list(newItems)
        # remove indexing of items to remove
        for ind in xrange(i,j):
            _del(_get(ind))
        # add new indexing
        if isinstance(newList, IndexedList):
            self._index.update(newList._index)
        else:
            for obj in newList:
                _add(obj)
        # replace items
        return list.__setslice__(self, i, j, newList)

    def append(self, obj):
        self._addindex(obj)
        return list.append(self, obj)

    def extend(self, newList):
        newList = list(newList)
        if isinstance(newList, IndexedList):
            self._index.update(newList._index)
        else:
            _add = self._addindex
            for obj in newList:
                _add(obj)
        return list.extend(self, newList)

    def insert(self, ind, new_obj):
        # ensure that ind is a numeric index
        try:
            obj = list.__getitem__(self, ind)
        except (IndexError, TypeError):
            obj = self._index[ind]
            ind = list.index(self, obj)
        self._addindex(new_obj)
        return list.insert(self, ind, new_obj)

    def pop(self, ind=-1):
        # ensure that ind is a numeric index
        try:
            obj = list.__getitem__(self, ind)
        except (IndexError, TypeError):
            obj = self._index[ind]
            ind = list.index(self, obj)
        self._delindex(obj)
        return list.pop(self, ind)

    def remove(self, ind_or_obj):
        try:
            obj = self._index[ind_or_obj]
            ind = list.index(self, obj)
        except KeyError:
            ind = list.index(self, ind_or_obj)
            obj = list.__getitem__(self, ind)
        self._delindex(obj)
        return list.remove(self, ind)

可以用作:

class Child(object):
    def __init__(self, id, name):
        self.id = id
        self.name = name

class Teacher(object):
    def __init__(self, id, name):
        self.id = id
        self.name = name

class Classroom(object):
    def __init__(self, children, teachers):
        self.children = IndexedList(children, ('id','name'))
        self.teachers = IndexedList(teachers, ('id','name'))

classroom = Classroom([Child('389','pete')], [Teacher('829','bob')])

print classroom.children[0].name               # -> pete

classroom.children.append(Child('2344','joe'))
print len(classroom.children)                  # -> 2
print classroom.children[1].name               # -> joe
print classroom.children['joe'].id             # -> 2344
print classroom.children['2344'].name          # -> joe

p = classroom.children.pop('pete')
print p.name                                   # -> pete
print len(classroom.children)                  # -> 1

编辑:我在一些异常处理中犯了一个错误(捕获 KeyError 而不是 IndexError)；它是固定的。我将添加一些单元测试代码。如果您遇到任何其他错误，请告诉我!