我想知道如何实现高级排序功能,这些功能可以作为元组元素传递给python'sorted'函数的键参数。
这是一个描述我想做什么的例子:
class Book:
def __init__(self, name, author, language, cost):
self.name = name
self.author = author
self.language=language
self.cost = cost
bookList = [list of books]
firstLanguage = "Armenian"
possibleLanguages = ["English", "Spanish", "Armenian", "French", "Chinese", "Swahili"]
possibleLanguages.remove("Armenian")
sortedBookList = sorted(bookList, key=(sortByName,
sortByFirstLanguage(firstLanguage), sortByLanguages(possibleLanguages) ))
基本上,我想实现上述的'sortByFirstLanguage'和'sortByLanguages'函数,以便将它们作为'key'参数的元组项传递给python'sorted'函数。这是一些有关自定义排序功能应如何的示例代码:
def sortByName(elem):
return elem.name
def sortByFirstLanguage(elem, firstLanguage):
if elem.language == firstLanguage:
return 1
else:
return -1
def sortByLanguages(elem, possibleLanguages):
if elem.language in possibleLanguages:
return possibleLanguages.index(elem.language)
我如何准确地告诉'key'参数将额外的参数'firstLanguage'&&'possibleLanguages'传递给自定义排序函数,如我上面所示?
正如Ashish在评论中所指出的那样,由于key
仅接受单个功能,因此我们首先需要组合这些功能。如果我们返回函数结果的序列(列表,元组),则Python将做正确的事情,仅在较早的元素相等(源)的情况下才比较较晚的元素(较右边的元素)。
我知道有几种方法可以做到这一点。
使用lambda:
sortedBookList = sorted(
bookList,
key=lambda elem: (sortByName(elem),
sortByFirstLanguage(elem, firstLanguage),
sortByLanguages(elem, possibleLanguages)))
使用高阶函数:
def key_combiner(*keyfuncs):
def helper(elem):
return [keyfunc(elem) for keyfunc in keyfuncs]
return helper
def sortByFirstLanguage(firstLanguage):
def helper(elem):
return elem.language == firstLanguage # True > False
return helper
def sortByLanguages(possibleLanguages):
def helper(elem):
if elem.language in possibleLanguages:
return possibleLanguages.index(elem.language)
return helper
sortedBookList = sorted(bookList,
key=key_combiner(sortByName,
sortByFirstLanguage(firstLanguage),
sortByLanguages(possibleLanguages))
Lambda对我来说似乎是最干净的,所以这可能就是我要使用的。
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我来说两句