帮助Python列表理解(Help with python list

帮助Python列表理解(Help with python list-comprehension)

我的问题的简化版本：

我有一个列表理解，我用它来设置二维列表上的位标记，所以：

s = FLAG1 | FLAG2 | FLAG3 [[c.set_state(s) for c in row] for row in self.__map]

所有set_state所做的是：

self.state |= f

这工作正常，但我必须在__map中的每个单元格中具有此函数“set_state”。 __map中的每个单元格都有一个.state，所以我想要做的是这样的：

[[c.state |= s for c in row] for row in self.map]

要么

map(lambda c: c.state |= s, [c for c in row for row in self.__map])

除此之外都不起作用（语法错误）。 也许我正在用map / lamda吠叫错误的树，但是我想摆脱set_state。 也许知道为什么赋值在列表理解中不起作用

A simplified version of my problem:

I have a list comprehension that i use to set bitflags on a two dimensional list so:

s = FLAG1 | FLAG2 | FLAG3 [[c.set_state(s) for c in row] for row in self.__map]

All set_state does is:

self.state |= f

This works fine but I have to have this function "set_state" in every cell in __map. Every cell in __map has a .state so what I'm trying to do is something like:

[[c.state |= s for c in row] for row in self.map]

or

map(lambda c: c.state |= s, [c for c in row for row in self.__map])

Except that neither works (Syntax error). Perhaps I'm barking up the wrong tree with map/lamda but I would like to get rid on set_state. And perhaps know why assignment does not work in the list-comprehension

最满意答案

是的，你正在使用错误的工具。 列表理解返回一个全新的值，所以你可以这样做：

self.__map = [[c.state | s for c in row] for row in self.__map]

但我的直觉是你应该只使用两个for循环：

for row in self.__map: for c in row: c.state |= s

在列表理解中，结果必须是表达式。 那是因为你的双重理解只是为了这个糖：

list1 = [] for row in self.__map: list2 = [] for c in row: list2.append(c.state | s) list1.append(list2) self.__map = list1

说没有意义

list2.append(c.state |= s)

因为最里面的表达式必须返回要附加到list2 。

基本上，每次更新标志时，列表解析都会创建自我.__映射的完整新副本。 如果这就是你想要的，那就去吧。 但我怀疑你只是想改变现有的地图。 在这种情况下，使用double for循环。

Yes, you're using the wrong tool. A list comprehension returns a completely new value, so you might be able to do this:

self.__map = [[c.state | s for c in row] for row in self.__map]

But my instinct is that you should just be using two for loops:

for row in self.__map: for c in row: c.state |= s

In a list comprehension, the result has to be an expression. That's because your double comprehension is just sugar for this:

list1 = [] for row in self.__map: list2 = [] for c in row: list2.append(c.state | s) list1.append(list2) self.__map = list1

It makes no sense to say

list2.append(c.state |= s)

Because the innermost expression has to return something to be appended to list2.

Basically, the list comprehensions make a complete new copy of self.__map each time you update the flags. If that's what you want, then go with it. But I suspect you just want to change the existing map. In that case, use the double for loops.