在 SORT 中使用 Lambda 作为 Key 函数

Question

我有一本以公司名称为键的字典。这些值是两个事物的命名元组。具有指向公司网址的链接和具有数值的等级的实体。我想根据价值特别是按等级对这本字典进行排序。我正在尝试将 key 函数用作 key=lambda (k,v):v.grade。但是我在 lambda 关键字旁边的括号处收到一个错误。代码 sn-p 如下。有人可以帮忙吗？

sorted_dict = sorted(list(dict_interested_companies.items()), key=lambda (k,v):v.grade)

例如显示dict.items()的值

[('Google', named_tuple(entity='http://money.cnn.com/video/technology/2018/02/01/kevin-abosch-i-am-a-coin.cnnmoney/index.html',grade=45)), ('Comcast', named_tuple(entity='http://money.cnn.com/2018/02/02/pf/college/public-service-student-loan-forgiveness/index.html',grade=39))

Answer 1

key 函数不应该有两个参数。它总是会接受一个论点。碰巧在这种情况下，参数是一个 2 元组，但它仍然是一个参数。

# This is a function taking two arguments,
# *not* a function taking a tuple.
lambda k, v: v.grade

# This is equivalent to the above in Python
# 2 but has been disallowed in Python 3. Don't
# use this syntax; it's not portable.
lambda (k, v): v.grade

# This is a function taking one argument, a tuple,
# and using its second element. This is what you want.
lambda x: x[1].grade

Answer 2

如果你想避免使用数字索引，你可以使用嵌套的 lambda 和 uppacking：

from collections import namedtuple

named_tuple = namedtuple('named_tuple', ['entity', 'grade'])

dict_interested_companies = {
    'Google': named_tuple(entity='http://money.cnn.com/video/technology/2018/02/01/kevin-abosch-i-am-a-coin.cnnmoney/index.html', grade=45),
    'Comcast': named_tuple(entity='http://money.cnn.com/2018/02/02/pf/college/public-service-student-loan-forgiveness/index.html', grade=39)
}

sorted_list = sorted(dict_interested_companies.items(), key=lambda item: (lambda key, value: value.grade)(*item))

print(sorted_list)

输出

[('Comcast', named_tuple(entity='http://money.cnn.com/2018/02/02/pf/college/public-service-student-loan-forgiveness/index.html', grade=39)), ('Google', named_tuple(entity='http://money.cnn.com/video/technology/2018/02/01/kevin-abosch-i-am-a-coin.cnnmoney/index.html', grade=45))]