Sort

1. >>>sorted([5,2,3,1,4])
   [1,2,3,4,5]
2. >>>a=[5,2,3,1,4]
   >>>a.sort()
   >>>a
   [1,2,3,4,5]
3. list.sort()只能應用在list上，但是sorted（）函數卻能接受別的類型。
   >>>sorted({1:'D',2:'B',3:'B',4:'E',5:'A'})
   [1,2,3,4,5]

4. >>> sorted("This is a test string from Andrew".split(), key=str.lower)
   ['a', 'Andrew', 'from', 'is', 'string', 'test', 'This']

   
   

5. >>> student_tuples = [
           ('john', 'A', 15),
           ('jane', 'B', 12),
           ('dave', 'B', 10),
   ]
   >>> sorted(student_tuples, key=lambda student: student[2])   # sort by age
   [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

   
   

6. >>> 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 student: student.age)   # sort by age
   [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

   
   

7. >>> from operator import itemgetter, attrgetter
   
   >>> 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)]

   itemgetter,attrgetter，在operator模塊裏，使用之前要import operator

8. >>> sorted(student_tuples, key=itemgetter(1,2))
   [('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]
   
   >>> sorted(student_objects, key=attrgetter('grade', 'age'))
   [('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]

   先比較第二項，再比較第三項。

9. >>> sorted(student_tuples, key=itemgetter(2), reverse=True)
   [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]
   
   >>> sorted(student_objects, key=attrgetter('age'), reverse=True)
   [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]

   可以接受一個reverse參數，可以變爲降序。

10. >>> data = [('red', 1), ('blue', 1), ('red', 2), ('blue', 2)]
    >>> sorted(data, key=itemgetter(0))
    [('blue', 1), ('blue', 2), ('red', 1), ('red', 2)]

    有同樣的key時，保持原來的順序。
    

    >>> s = sorted(student_objects, key=attrgetter('age'))     # sort on secondary key
    >>> sorted(s, key=attrgetter('grade'), reverse=True)       # now sort on primary key, descending
    [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

    先按grade升序，再按成績降序。