sorted(iterable[, cmp[, key[, reverse]]])
iterable.sort(cmp[, key[, reverse]])
Parameter interpretation ：
（1）iterable Specify the to sort list perhaps iterable, Needless to say ;
（2）cmp For the function , Specify the function to compare when sorting , You can specify a function or lambda function , Such as ：
students For class objects list, No member has three domains , use sorted When comparing, you can decide by yourself cmp function , For example, here we want to sort by comparing the third data member , The code can be written like this ：
students = [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]
sorted(students, key=lambda student : student[2])
（3）key For the function , Specifies which item of the element to be sorted is to be sorted , The function is illustrated by the above example , The code is as follows ：
sorted(students, key=lambda student : student[2])
key designated lambda The function function is to remove elements student The third domain of （ namely ：student[2]）, therefore sorted Sorting time , Will students The third field of all elements to sort .
1. Order of original address
1） The list has its own sort Method , It sorts the list in its original location , Since it's in the original order , It's obviously impossible to have this method , Because tuples are immutable .
x = [4, 6, 2, 1, 7, 9]
x.sort()
print (x) # [1, 2, 4, 6, 7, 9]
2. Replica sort
1）[:] Fragmentation method
x =[4, 6, 2, 1, 7, 9]
y = x[ : ]
y.sort()
print (y) #[1, 2, 4, 6, 7, 9]
print (x) #[4, 6, 2, 1, 7, 9]
Be careful ：y = x[:] List by slicing x All the elements of are copied to y, If you simply put x Assign a value to y：y = x,y and x Or point to the same list , No new copy is generated .
2）sorted Method
sorted Return an ordered copy , And the type is always a list , as follows ：
x =[4, 6, 2, 1, 7, 9]
y = sorted(x)
print (y) #[1, 2, 4, 6, 7, 9]
print (x) #[4, 6, 2, 1, 7, 9]
print (sorted('Python')) #['P', 'h', 'n', 'o', 't', 'y']
1. Customize cmp Comparison function
def comp(x, y):
if x < y:
return 1
elif x > y:
return -1
else:
return 0
nums = [3, 2, 8 ,0 , 1]
nums.sort(comp)
print (nums) # null [8, 3, 2, 1, 0]
nums.sort(cmp) # Call built-in functions cmp , Ascending sort
print (nums) # null [0, 1, 2, 3, 8]
2. Customize key and reverse
（1.reverse Implement descending sort , You need to provide a Boolean value , The default is False（ Ascending order ）.
（2.key When using, you must provide a function that is always called by the sorting process ：
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alist = [('2', '3', '10'), ('1', '2', '3'), ('5', '6', '7'), ('2', '5', '10'), ('2', '4', '10')]
# Multi level sorting , First, according to paragraph 3 Order of elements , Then according to the 2 Order of elements ：
print (sorted(alist, cmp = None, key = lambda x:(int(x[2]), int(x[1])), reverse = False))
-------------------------------------------------------------------------------------------
[('1', '2', '3'), ('5', '6', '7'), ('2', '3', '10'), ('2', '4', '10'), ('2', '5', '10')]
operator Module provided itemgetter Function is used to get the data of which dimensions of an object , The parameter is some sequence number （ That is, the serial number of the data to be acquired in the object ）, Let's take an example .
a = [1,2,3]
>>> b=operator.itemgetter(1) // Defined function b, Get the... Of the object 1 Values for domains
>>> b(a)
2
>>> b=operator.itemgetter(1,0) // Defined function b, Get the... Of the object 1 Domain and the 0 The value of
>>> b(a)
(2, 1)
it is to be noted that ,operator.itemgetter Function does not get value , It defines a function , This function is used to get the value of an object .
itemgetter stay sort In the middle of the day ：
from operator import itemgetter
alist = [('2', '3', '10'), ('1', '2', '3'), ('5', '6', '7'), ('2', '5', '10'), ('2', '4', '10')]
# Multi level sorting , First, according to paragraph 3 Order of elements , Then according to the 2 Order of elements ：
print (sorted(alist, cmp = None, key = itemgetter(2, 1), reverse = False))
print (sorted(alist, cmp = None, key = lambda x:itemgetter(2, 1)(x), reverse = False))
print (sorted(alist, cmp = None, key = lambda x:map(int, itemgetter(2, 1)(x)), reverse = False))
-------------------------------------------------------------------------------------------------
[('2', '3', '10'), ('2', '4', '10'), ('2', '5', '10'), ('1', '2', '3'), ('5', '6', '7')]
[('2', '3', '10'), ('2', '4', '10'), ('2', '5', '10'), ('1', '2', '3'), ('5', '6', '7')]
[('1', '2', '3'), ('5', '6', '7'), ('2', '3', '10'), ('2', '4', '10'), ('2', '5', '10')]
