Question

关于嵌套循环的简单问题。

stocks = {'GE': 6.28, 'XOM': 39.8}
for quote in stocks.values():
    print(quote)

    for symbol in stocks.keys():
        print(symbol)

        print('You have purchased', symbol, 'for', quote)

输出：

GE
You have purchased GE for 39.8
XOM
You have purchased XOM for 39.8

为什么说明GE是在39.8而不是6.28购买的？我试图缩进和缩进循环代码，但是没有运气。请帮忙吗？

Answer 1

如果您要打印字典的键和值，则只需将它们解压缩为一个for循环即可：

for symbol, quote in stocks.items():
    print(symbol)
    print('You have purchased', symbol, 'for', quote)

Answer 2

字典通常没有排序。

您将需要按照与遍历相同的顺序进行打印：

class MyEventsPage extends StatefulWidget {
  MyEventsPage({Key key}) : super(key: key);

  @override
  _MyEventsPageState createState() => _MyEventsPageState();
}

class _MyEventsPageState extends State<MyEventsPage>
    with AutomaticKeepAliveClientMixin<MyEventsPage> {
  Completer<void> _refreshCompleter;
  PaginatedEvent _paginated;
  MyEventsBloc _myEventsBloc;
  bool _isFetchingMoreInBackground;

  @override
  void initState() {
    super.initState();
    _myEventsBloc = BlocProvider.of<MyEventsBloc>(context);
    _myEventsBloc.add(MyEventsPageInitialized());
    _refreshCompleter = Completer<void>();
    _isFetchingMoreInBackground = false;
  }

  void _set(PaginatedEvent paginated) {
    setState(() {
      _paginated = paginated;
    });
    _refreshCompleter?.complete();
    _refreshCompleter = Completer();
  }

  void _add(Event data) {
    setState(() {
      _paginated.data.add(data);
    });
  }

  void _update(Event data) {
    final int index = _paginated.data.indexWhere((leave) {
      return leave.id == data.id;
    });

    setState(() {
      _paginated.data[index] = data;
    });
  }

  void _destroy(Event data) {
    final int index = _paginated.data.indexWhere((leave) {
      return leave.id == data.id;
    });

    setState(() {
      _paginated.data.removeAt(index);
    });
  }

  void _append(PaginatedEvent paginated) {
    setState(() {
      _paginated.currentPage = paginated.currentPage;
      _paginated.data.addAll(paginated.data);
    });
  }

  bool _onScrollNotification(ScrollNotification notification) {
    if (notification is! ScrollEndNotification) return false;

    print('extentBefore: ${notification.metrics.extentBefore}');
    print('extentAfter: ${notification.metrics.extentAfter}');
    print('maxScrollExtent: ${notification.metrics.maxScrollExtent}');
    return true;
  }

  @override
  Widget build(BuildContext context) {
    super.build(context);
    return RefreshIndicator(
      onRefresh: () {
        _myEventsBloc.add(MyEventsRefreshRequested());
        return _refreshCompleter.future;
      },
      child: NotificationListener<ScrollNotification>(
        onNotification: _onScrollNotification,
        child: CustomScrollView(
          slivers: [
            SliverOverlapInjector(
              handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
            ),
            SliverToBoxAdapter(
              child: BlocConsumer<MyEventsBloc, MyEventsState>(
                listener: (context, state) {
                  if (state is MyEventsLoadSuccess) {
                    _set(state.data);
                  }

                  if (state is MyEventsCreateSuccess) {
                    _add(state.data);
                  }

                  if (state is MyEventsUpdateSuccess) {
                    _update(state.data);
                  }

                  if (state is MyEventsDestroySuccess) {
                    _destroy(state.data);
                  }

                  if (state is MyEventsLoadMoreSuccess) {
                    _append(state.data);
                  }
                },
                builder: (context, state) {
                  if (state is MyEventsLoadSuccess) {
                    return EventList(data: _paginated.data);
                  }

                  return ListLoading();
                },
              ),
            ),
          ],
        ),
      ),
    );
  }

  @override
  bool get wantKeepAlive => true;
}

Answer 3

这是python中字典的推荐迭代。

stocks = {'GE': 6.28, 'XOM': 39.8}
for key,value in stocks.items():
  print('You have purchased', key, 'for', value)

简单的嵌套循环？

3 个答案: