list.sort() modifies the list in-place, the list.sort() method is only defined for lists.
sorted() build a new sorted list from an iterable （数组/字符串/列表/集合/字典）, the sorted() function accepts any iterable.
Sorting Basics
list.sort() and sorted() 按照 lexicographically 字典序 进行，参照
http://besideme.github.io/jekyll/update/2015/09/12/Python-data-structure.html
sorted("this is A test".split())
['A','is','test','this']
# 如果不加 split() 函数，则输出为 [' ',' ',' ','A','e','h','i','i',...]
sorted(set(['a','eee','bfrr']))
['a','bfrr','eee']Key Functions
>>> student_tuples = [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]
>>> sorted(student_tuples, key = lambda stu: stu[2]) # sort by age
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]class Student:
def __init__(self, name, grade, age):
self.name = name
self.grade = grade
self.age = age
def __repr__(self):
return repr((self.name, self.grade, self.age))
>>> student_objects = [
Student('john', 'A', 15),
Student('jane', 'B', 12),
Student('dave', 'B', 10)
]
>>> sorted(student_objects, key = lambda stu: stu.age) # sort by age
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]Operator Module Functions
operator.itemgetter(), operator.attrgetter() can be easier
>>> from operator import itemgetter, attrgetter,methodcaller
>>> sorted(student_tuples, key = itemgetter(2))
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
>>> sorted(student_objects, key = attrgetter('age'))
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]The operator module functions allow multiple levels of sorting.
For example, to sort by grade then by age
That means if grades are the same then compare age
>>> sorted(student_tuples, key = itemgetter(1,2))
[('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]
>>> sorted(student_objects, key = attrgetter('grade', 'age'))The operator.methodcaller() function makes method calls with fixed parameters for each object being sorted.
For example, the str.count() method could be used to compute message priority by counting the number of exclamation marks in a message
>>> m = ['aa', 'de', 'ad']
>>> sorted(m, key = methodcaller('count', 'a'))
['de', 'ad', 'aa']Ascending and Descending
reverse = True，逆序
or a.reverse()
sorted(student_tuples, key=itemgetter(2), reverse=True)Sort Stability and Complex Sorts
Starting with Python 2.2, sorts are guaranteed to be stable. That means that when multiple records have the same key, their original order is preserved.
This wonderful property lets you build complex sorts in a series of sorting steps. For example, to sort the student data by descending grade and then ascending age, do the age sort first and then sort again using grade．
Odd and Ends
Key functions need not depend directly on the objects being sorted. A key function can also access external resources. For instance, if the student grades are stored in a dictionary, they can be used to sort a separate list of student names.
>>> students = ['dave', 'john', 'jane']
>>> grades = {'john': 'F', 'jane':'A', 'dave': 'C'}
>>> sorted(students, key=grades.__getitem__)
['jane', 'dave', 'john']
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