Sort the list of instances in Python

Many times we need to sort the list, and Python provides two ways to sort a given list L:

Method 1: Sort by the member function of list
Method 2: Sort using the built-in function sorted (starting from 2.4)

These two methods are similar in use, with the first example being explained:

Starting with Python2.4, the sort method has three optional parameters, as described in the Python Library reference

The code is as follows:

CMP:CMP Specifies a custom comparison function of the arguments (iterable elements) which should return a negative, zero O R positive number depending on whether the first argument are considered smaller than, equal to, or larger than the second Argument
"Cmp=lambda x,y:cmp (X.lower (), Y.lower ())"
Key:key specifies a function of one argument that's used to extract a comparison key from each list element: "Key=str.low Er
Reverse:reverse is a Boolean value. If set to True, then the list elements is sorted as if each comparison were reversed. In general, the key and reverse conversion processes is much faster than specifying an
Equivalent CMP function. This is because CMP are called multiple times for each list element while keys and reverse touch each element only once.

The following is a concrete example of sort.
Example 1:

The code is as follows:

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

Example 2:

The code is as follows:

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

Example 3:

The code is as follows:

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

Example 4:

The code is as follows:

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

Example 5:

The code is as follows:

>>>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)

The code is as follows:

>>>l = [(' B ', 2), (' A ', 1), (' C ', 3), (' d ', 4)]
>>>a = [(x[1],i,x) for i,x in Enumerate (L)] #i can confirm the stable 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:

The code is as follows:

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:

The code is as follows:

>>>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 ordered L is sorted only by the second keyword, if we want to use the second keyword
Sort by the first keyword after ordering? There are two ways
Example 8:

The code is as follows:

>>> 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:

The code is as follows:

>>> 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 one, if
Equal, compare the second one

