[英]How to pass additional arguments to custom python sorting function
I would like to know how I can implement advanced sorting functions that I can pass in as tuple element to the key argument of the python 'sorted' function. 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。
Here is an example depicting what I would like to do: 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) ))
Basically I would like to implement the 'sortByFirstLanguage' and 'sortByLanguages' functions described above so that I can pass them to the python 'sorted' function as the tuple items of the 'key' argument. 基本上,我想实现上述的'sortByFirstLanguage'和'sortByLanguages'函数,以便可以将它们作为'key'参数的元组项传递给python'sorted'函数。 Here is some example code regarding what the custom sort functions should look like:
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)
How exactly can I tell the 'key' argument to pass in the extra arguments 'firstLanguage' && 'possibleLanguages' to custom sorting functions as I have shown above? 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?
As Ashish points out in the comments, we first need to combine these functions, since key
only accepts a single functions. 正如Ashish在评论中指出的那样,我们首先需要组合这些功能,因为
key
只接受一个功能。 If we return a sequence (list, tuple) of the function results, Python will do the right thing, only comparing later (farther right) elements if the earlier elements are equal ( source ). 如果我们返回函数结果的序列(列表,元组),Python会做正确的事情,只有在较早的元素相等时才比较较晚的元素( 源 )。
I know of a couple ways to do this. 我知道有几种方法可以做到这一点。
Using lambdas: 使用lambda:
sortedBookList = sorted(
bookList,
key=lambda elem: (sortByName(elem),
sortByFirstLanguage(elem, firstLanguage),
sortByLanguages(elem, possibleLanguages)))
Using higher-order functions: 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))
Lambdas seem cleanest to me, so that's probably what I'd use. 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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