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

pythonThere are three list sorting methods in the language: reverse/reverse sorting, sortForward sorting, and sorted can obtain the sorted list. In more advanced list sorting, the latter two methods can also add conditional parameters for sorting.

reverse() method

Reverse the sorting 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 sorting of the list: the order of the elements in the original list is from the left Restore to the right without sorting the parameters in the list. 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 is directly Modify 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, variableb gets: A null value. So what should you do if you want to get a sorted list but want to keep the original list? The list sorted() method can help you achieve this.

sorted() method

You can keep 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 sequence of data type , what is returned is always a list form:

>>> 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 variable object (dictionary, list ) method, no parameters, no return value, sort() will change the mutable object, so there is no need to return a value. 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 python's built-in function, and is not a unique method of variable objects (lists, dictionaries). The sorted() function requires A parameter (the parameter can be a list, dictionary, tuple, or string). No matter what parameter is passed, a return value with a list as a 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

The "reversal" effect can also be achieved by slicing the sequence

>>> 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]

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