Detailed explanation of Python list sorting methods reverse, sort, sorted

There are three list sorting methods in the Python language: reverse/reverse sorting, sort forward sorting, and sorted to obtain the sorted list. In more advanced list sorting, the latter two methods can also add conditional parameters for sorting. The

reverse() method

reverses the order of the elements in the list, such as the following

>>> x = [1,5,2,3,4]
>>> x.reverse()
>>> x
[4, 3, 2, 5, 1]

reverse list reverse sorting: It re-stores the elements in the original list from left to right instead of The parameters in the list will be sorted. If you need to sort the parameters in the list, you need to use sort, another sorting method for the list, to sort in positive order.

sort() sorting method

This function method performs forward sorting of the list contents. The sorted new list will overwrite the original list (the id remains unchanged), that is, the sort sorting method directly modifies the original list list sorting method.

>>> a = [5,7,6,3,4,1,2]
>>> a.sort()
>>> a
[1, 2, 3, 4, 5, 6, 7]

Many python beginners are confused about the sort() method. Sometimes they need a sorted list, but want to save the original unsorted list. They will do this:

>>> a = [5,7,6,3,4,1,2]
>>> b = a.sort()
>>> print b
None

The problem arises at this time, the variable b gets a null value. So what should I do if I want to get the sorted list but also want to keep the original list? The list sorted() method can help you achieve this.

sorted() method

can retain the original list and get the sorted list. The sorted() operation method is as follows:

>>> a = [5,7,6,3,4,1,2]
>>> b = sorted(a)
>>> a
[5, 7, 6, 3, 4, 1, 2]
>>> b
[1, 2, 3, 4, 5, 6, 7]

sorted() method can be used in any data type sequence, What is always returned is in the form of a list:

>>> sorted('iplaypython.com')
['.', 'a', 'c', 'h', 'i', 'l', 'm', 'n', 'o', 'o', 'p', 'p', 't', 'y', 'y']

The difference between the three

sort() is a method of variable objects (dictionaries, lists), with no parameters and no return value. sort() will change the variable Object, so no return value is required. The sort() method is a method or attribute unique to mutable objects. Immutable objects such as tuples and strings do not have these methods. If called, an exception will be returned.

>>> a=[5,4,3,2,1]
>>> a.sort()
>>> 
>>> a
[1, 2, 3, 4, 5]

sorted() is a built-in function of Python and is not a unique method of mutable objects (lists and dictionaries). The sorted() function requires a parameter (the parameter can be a list, dictionary, tuple, character String), no matter what parameters are passed, a return value with a list as the container will be returned. If it is a dictionary, a list of keys will be returned.

>>> mystring="54321"
>>> mytuple=(5,4,3,2,1)
>>> mylist=[5,4,3,2,1]
>>> sorted(mystring)
['1', '2', '3', '4', '5']
>>> sorted(mytuple)
[1, 2, 3, 4, 5]
>>> sorted(mylist)
[1, 2, 3, 4, 5]

reverse() is used in the same way as sort, and reversed() is used in the same way as sorted()

>>> mylist=[5,4,3,2,1]
>>> mylist.reverse()
>>> mylist
[1, 2, 3, 4, 5]
>>> mylist=[5,4,3,2,1]
>>> for i in reversed(mylist):
...   print i,
... 
1 2 3 4 5

"Reversal" can also be achieved by slicing the sequence The effect of

>>> mystring="54321"
>>> mytuple=(5,4,3,2,1)
>>> mylist=[5,4,3,2,1]
>>> mystring[::-1]
'12345'
>>> mytuple[::-1]
(1, 2, 3, 4, 5)
>>> mylist[::-1]
[1, 2, 3, 4, 5]