Two methods and examples of Python list sorting

To sort the list, Python provides two methods

Method 1: Sort by using the list's built-in function list.sort

List.sort (Func=none, Key=none, Reverse=false)

Python instance:

>>> list = [2,5,8,9,3]  >>> list  [2,5,8,9,3]  >>> list.sort ()  >>> List  [2, 3, 5, 8, 9]

Method 2: Sort by Sequence type function sorted (list) (starting from 2.4)

Python instance:

>>> list = [2,5,8,9,3]  >>> list  [2,5,8,9,3]  >>> sorted (list)  [2, 3, 5, 8, 9]

The difference between the two methods:

Sorted (list) Returns an object that can be used as an expression. The original list does not change, creating a new sorted list object.

List.sort () does not return an object, changing the original list.

Other examples of sort:

Example 1: Forward Ordering

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

Example 2: Reverse sorting

>>>l = [2,3,1,4]>>>l.sort (reverse=true) >>>l>>>[4,3,2,1]

Example 3: Sort the second keyword

>>>l = [(' B ', 6), (' A ', 1), (' C ', 3), (' d ', 4)]>>>l.sort (Lambda x,y:cmp (x[1],y[1])) >>>L> >>[(' A ', 1), (' C ', 3), (' d ', 4), (' B ', 6)]

Example 4: Sort the second keyword

>>>l = [(' B ', 6), (' A ', 1), (' C ', 3), (' d ', 4)]>>>l.sort (Key=lambda x:x[1]) >>>l>>>[( ' A ', 1), (' C ', 3), (' d ', 4), (' B ', 6)]

Example 5: Sort the second keyword

>>>l = [(' B ', 2), (' A ', 1), (' C ', 3), (' d ', 4)]>>>import Operator>>>l.sort (key= Operator.itemgetter (1)) >>>l>>>[(' A ', 1), (' B ', 2), (' C ', 3), (' d ', 4)]

Example 6: (DSU method: Decorate-sort-undercorate)

>>>l = [(' B ', 2), (' A ', 1), (' C ', 3), (' d ', 4)]>>>a = [(x[1],i,x) for i,x in Enumerate (L)] #i can confirm the s Table Sort>>>a.sort () >>>l = [s[2] for S in a]>>>l>>>[(' A ', 1), (' B ', 2), (' C ', 3), (' D ', 4)]

The above gives the method of sorting the list in 6, where instance 3.4.5.6 can play an item in the list item

Sort the comparison keywords.

Efficiency comparison:

CMP < DSU < key

Comparing with the experiment, Method 3 is slower than method 6, method 6 is slower than Method 4, Method 4 and Method 5 are basically equivalent

Multi-keyword comparison sort:

Example 7:

>>>l = [(' d ', 2), (' A ', 4), (' B ', 3), (' C ', 2)]>>> L.sort (Key=lambda x:x[1]) >>> l>>>[( ' d ', 2), (' C ', 2), (' B ', 3), (' A ', 4)]

As we can see, the sort of L is now sorted by the second keyword only,

What if we want to order the second keyword and then sort it with the first keyword? There are two ways

Example 8:

>>> L = [(' d ', 2), (' A ', 4), (' B ', 3), (' C ', 2)]>>> L.sort (Key=lambda x: (X[1],x[0])) >>> l> >>[(' C ', 2), (' d ', 2), (' B ', 3), (' A ', 4)]

Example 9:

>>> L = [(' d ', 2), (' A ', 4), (' B ', 3), (' C ', 2)]>>> L.sort (Key=operator.itemgetter (1,0)) >>> L >>>[(' C ', 2), (' d ', 2), (' B ', 3), (' A ', 4)]

Why does instance 8 work? The reason is that a tuple is compared from left to right, compared to the first, if

Equal, compare the second one

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