python的代码不理解，题很简单，只是这种解法不懂

Question

实现一个函数likes :: [String] -> String，该函数必须接受输入数组，
其中包含喜欢某个项目的人的姓名。它必须返回显示文本，如示例所示：

1. likes([]) # must be "no one likes this"
2. likes(["Peter"]) # must be "Peter likes this"
3. likes(["Jacob", "Alex"]) # must be "Jacob and Alex like this"
4. likes(["Max", "John", "Mark"]) # must be "Max, John and Mark like this"
5. likes(["Alex", "Jacob", "Mark", "Max"]) # must be "Alex, Jacob and 2 others like this"

def likes(names):
    n = len(names)
    return {
        0: 'no one likes this',
        1: '{} likes this',
        2: '{} and {} like this',
        3: '{}, {} and {} like this',
        4: '{}, {} and {others} others like this'
    }[min(4, n)].format(*names[:3], others=n-2)  #这一行不懂
print(likes(["Alex", "Jacob", "Mark", "Max", "Mark", "Max", "Mark", "Max"]))

输出 Alex, Jacob and 6 others like this

Answer 1

我将代码分解了一下，并加上了注释，应该可以让你看懂。

def likes(names):
    n = len(names)
    temp = {
        0: 'no one likes this',
        1: '{} likes this',
        2: '{} and {} like this',
        3: '{}, {} and {} like this',
        4: '{}, {} and {others} others like this'
    }
    # 找到当前len的对应的返回格式
    text = temp[min(n, 4)]

    # 之后是format方法
    # 假如熟悉str的format方法的话，看下面的注释应该可以理解
    
    # *names[:3]   ==> 取前3位，因为len=3时，要取3位，*用于解包，取多了不会填进去
    #                  而且，["Alex", "Jacob"][:3]这种情况也不会报错，取：["Alex", "Jacob"]
    # others=n - 2 ==> 用于给“{others}”格式化的，没有{others}时，也不会填进去
    
    return text.format(*names[:3], others=n - 2)


print(likes(["Alex", "Jacob", "Mark", "Max", "Mark", "Max", "Mark", "Max"]))

Answer 2

[min(4, n)] 取出對應格式化字符串，人數大於4都用第五個格式化字符串。

.format(*names[:3], others=n-2) 中的 *names[:3] 是將 names 數組切片，取出前三個，然後 * 展開作爲參數。 others=n-2 就是給第五個格式化字符串用的。

Answer 3

def likes(names):
    n = len(names)
    return {
        0: 'no one likes this',
        1: '{} likes this',
        2: '{} and {} like this',
        3: '{}, {} and {} like this',
        4: '{}, {} and {others} others like this'
    }[min(4, n)].format(*names[:3], others=n - 2)  # 这一行不懂
    # min(4, n) 最大值是4
    """
    {
        0: 'no one likes this',
        1: '{} likes this',
        2: '{} and {} like this',
        3: '{}, {} and {} like this',
        4: '{}, {} and {others} others like this'
    }[min(4, n)]
    字典取值，例如：
    {
        0: 'no one likes this',
        1: '{} likes this',
        2: '{} and {} like this',
        3: '{}, {} and {} like this',
        4: '{}, {} and {others} others like this'
    }[4]='{}, {} and {others} others like this'
    """
    # 然后是字符的format,字符串格式化
    # *names[:3] 先看names[:3]，取前三位，因为上面最多就用3个，所以这里取三位，format就算传多了也只会使用能用到的
    # 然后*就是转换一下传递方式， 参考：*args,**kwargs函数接值
    # others 是指定值传递，直接付给{others},如果前面没有{others}也不影响
    '{}, {} and {others} others like this'.format(*names[:3], others=n - 2)


print(likes(["Alex", "Jacob", "Mark", "Max", "Mark", "Max", "Mark", "Max"]))