To talk copy of the list, we will talk about Python assignment rules
First we create a list of a:
a=[1,2,3]
Usually we copy an element method is this:
= B A # copy element general procedure Print (A) Print (B) the result is: [ 2,3 ] [ 2,3]
By this line of code, we of course have created a list with the equivalent list a b, but this time it will be a problem :
When we try to create a new list of b when sorting operations (such as reverse operation):
b.reverse () Print (B) the result is: [ 3,2,1]
Everything here seems nothing wrong, but in reality pit father thing has quietly ~
Let us try to print it lists a value of :
Print (A) results: [ 3,2,1]
Can see a list of a sort also changed the
This is not necessarily the result we want to see
The reason for this is:
When we use the "b = a" code to assign this list b, b and list is a list point to the same address, and to sort the list operation does not assign a new address list, that this whether we are on a list or sort operation on the list b, ordering another list will change
And if we do an assignment or if the list for a list of b, then there is no such concerns, because when the assignment list is assigned a new address
So how do we solve this problem?
Very simple, just use the list of fragments using the following code listing the copy operation:
= A [2,3 ] B = A [:] # replication list right way Print (A) Print (B) the result is: [ 2,3 ] [ 2,3]
At this point we'll be on the list b reverse operation:
b.reverse () Print (A) Print (B) the result is: [ 2,3 ] [ 3,2,1]
Only you can see a list of b sort of change, and a list of the sort has not changed, it is because the list of a list of b and has no kind of helpless and tangled fetters of ( 
Ya Ya ◡ )