Collections in Python

Collection : Used to contain a set of unordered objects ;

It can be understood that putting a list in {} makes up a collection

Create a collection : Use the Set function or use {} and provide the item to be stored, such as:

s = set ([3,5,9,10]) #创建一个数据集合e = {1,2,3,4,6,7,8} #也可以这样创建一个数据集合t = set (' Hello ') #创建一个唯一字符的集合

Differences from lists and tuples:

1, the collection is unordered

2, cannot be indexed by number

3, the collection element cannot be repeated each element is unique

Check the values in the T collection:

Print (t)

Output a set of unordered:

{' H ', ' o ', ' e ', ' l '}

The collection supports a range of standard operations, including the set, intersection, difference set, and symmetric difference sets such as:

A = T|s #求并集b = T&s #求交集c = S-t #求差集d = t ^s # symmetric difference set

Explain:

| : Two merged objects of a collection

&: Two objects that exist at the same time as a collection

- : item exists in t but does not exist in S

^ :  Two objects in a collection that do not exist concurrently

Output Result:

{3, 4, 5, 6, 7, ' e ', ' l ', ' H ', ' O '}
Set ()
{' H ', ' l ', ' e ', ' O '}
{3, 4, 5, 6, 7, ' e ', ' o ', ' H ', ' l '}

Two ways to add data to a collection:

1,add () Method: Add an item

data = {1,2,3,4,5};d ata.add (6);p rint (data);

Output Result:

{1, 2, 3, 4, 5, 6}

2,update () Method: Add multiple items

Data.update (' ABC ');

#也可以使用 data.update (' A ', ' B ', ' C ');

Output Result:

{1, 2, 3, 4, 5, 6, ' A ', ' B ', ' C '}

method of deleting an item in the collection:

Remove () Method:

Data.remove (' A ');

Output Result:

{1, 2, 3, 4, 5, 6, ' B ', ' C '}

question: Why should there be a collection ?

Practice:

In the list, if you want to remove duplicates:

data = [' A ', ' B ', ' a ', ' C ', 1,2,3,2,4,1,3];all = [];for num in data: The #循环data数据 if num not in all: #如果不存在于列表all中 All.append (nu m); #则追加print (All);

Output Result:

{1, 2, 3, 4, ' A ', ' B ', ' C '}

to use the collection simplification list to remove the weight :

data = List (set (data));p rint (data);

explain : Because the objects in the collection are unique, the data declaration becomes a collection after the duplicates are removed and then converted to the list

Note : Because the set is unordered, the resulting sequence of results changes and is used with caution when the output order is specified

Output Result:

{1, 2, ' B ', ' C ', 3, ' A ', 4}

Summarize:

1, How to create a collection: Set () {}

2, the difference between a collection and a list, a tuple: unordered cannot index and slice objects are unique

3, how to find the intersection difference set symmetric difference set (|,&,-,^)

4, two ways to add and one way to delete: Add (), update (), remove ()

5, Practice: How to Use Collections: List (set (data));

This article is from the "Hong Dachun Technical column" blog, please be sure to keep this source http://hongdachun.blog.51cto.com/9586598/1761121

Collections in Python