Python Introductory Tutorials 03 list, Yuan Zu, collection, dictionary __python

This is the third of the Python introductory tutorials, which will specifically describe the four types of data structures commonly used in Python, which are lists, tuples, collections, dictionaries, which are often used later, so you need to understand each of these data structures.

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Python list, Yuan Zu, collection, dictionary

In this article we will talk about four kinds of data structures, lists, meta ancestors, collections, dictionaries, which are commonly used in Python.

· List []

· Tuple ()

· set {}

· dict {Key:value}

Lists List

Defined

Animals = [' Tiger ', ' Bear ', ' lion ']

Add-append at end

Call the Append method to add an element to the end of the list

Animals.append (' horse ')

Animals

[' Tiger ', ' Bear ', ' lion ', ' horse ']

Index

We can access each element of the list by index, the index of the first element is 0, and the index of the last element is-1

Animals[0]

' Tiger '

ANIMALS[-1]

' Horse '

We can use Len to get the list length

Len (Animals)

4

Add –insert Anywhere

Above we said append is added to the end of the list, and we can add the insert to any location in the list.

Animals.insert (1, ' Eagle ')

Animals

[' Tiger ', ' Eagle ', ' bear ', ' lion ', ' horse ']

Delete any specified value

We use remove to remove the specified value

Animals.remove (' Tiger ')

Animals

[' Eagle ', ' bear ', ' lion ', ' horse ']

Note: If Tiger appears more than once, only the first tiger will be deleted

Delete a keyword by index

Del Animals[1]

Animals

[' Eagle ', ' lion ', ' horse ']

List reversal

We want to remember that the list is orderly, and this can be compared to other data structures, so we can reverse the ordered list

Animals.reverse ()

Animals

[' Horse ', ' lion ', ' Eagle ']

Merge of Lists

Animals.extend ([' Tiger ', ' Bear '])

Animals

[' Horse ', ' lion ', ' Eagle ', ' tiger ', ' Bear ']

Find

Animals.index (' Lion ') #返回索引

1

Animals.count (' Lion ') #返回出现次数

1

' Lion ' inanimls# return Boolean type

True

Modify

Animals[0] = ' horses '

Animals

[' Horses ', ' lion ', ' Eagle ', ' tiger ', ' Bear ']

Use of POPs

The pop returns the last element of the list, and the element is also deleted when it is returned, and if you pass in a parameter pop (i), the first element pops up

For I inrange (len (Animals)):

Animal = Animals.pop ()

Print (animal) #把整个列表倒叙输出

>

Bear

Tiger

Eagle

Lion

Horses

Animals #此时列表是空的

[]

Animals.append (' Tiger ') #我们可以往里面添加值

Animals

[' Tiger ']

List multiplication

List1 = [1,2,3]

List1*3

[1, 2, 3, 1, 2, 3, 1, 2, 3] #列表重复三次

Ganso Tuple

Ganso is a special kind of list, the difference is ganso once created cannot be modified, the actions such as sort (), append () and so on Ganso are not applicable.

When writing a program, the meta ancestor is more secure than the list, if it is read-only data, use the meta ancestor as much as possible.

Create a meta ancestor

Animals = (' Tiger ', ' lion ', ' bear ')

Attention

If you create a ganso with only one element, you need to follow the element followed by a comma

Animals = (' tiger ')

Type (animals) #可以看到这里是str类型

Str

Animals

' Tiger '

Animals = (' Tiger ',)

Type (animals)

Tuple

Animals

(' Tiger ',)

Set Set

A collection is a unordered, distinct set of data, which, first of all, is unordered, cannot be accessed using an index, and another feature is that there is no duplication of data

The collection supports some mathematical operations, such as union (and set), intersection (intersection), difference (complement)

Creation of collections

Creation of a collection using the Set function or {}, note that the creation of an empty collection can only use the Set function, and an empty dictionary is created using {}.

Animals ={' tiger ', ' Bear ', ' lion ', ' Eagle ', ' Tiger '}

Animals

{' Bear ', ' Eagle ', ' lion ', ' tiger '} #可以看到重复的元素已经被去除

Animals =set ([' Tiger ', ' Bear ', ' lion ', ' Eagle ', ' Tiger '])

Type (animals)

Set

Animals

{' Bear ', ' Eagle ', ' lion ', ' tiger '} #可以看到重复的元素已经被去除

To see if an element is in the collection

' Tiger ' in animals

True

' Tigers ' in animals

False

' Tigers ' not in animals #注意这里是 not in

True

Additions and deletions of collections

Animals.add (' horse ')

Animals

{' Bear ', ' Eagle ', ' horse ', ' lion ', ' tiger '}

Animals.remove (' horse ')

Animals

{' Bear ', ' Eagle ', ' lion ', ' tiger '}

Concept of Set Subset

<=– belongs to

Set1 ={1,2,3}

Set2 ={2,3}

Set2 Inset1

False #思考这是为什么

Set2 <=set1

True

The operation of a set

Set1 = {1,2,3,4}

Set2 ={3,4,5,6}

· | Action, there are elements in the Set1 or Set2, equivalent to the Union operation

Set1|set2

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

Set1.union (Set2)

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

· & Operations, returning elements that are in Set1 and Set2

Set1&set2

{3,4}

· -Returns elements that are not set2 in Set1

Set1-set2

{1,2}

· ^ operations, returning elements that only exist in two collections

Set1^set2

{1,2,5,6}

Dictionary Dict

A dictionary is a collection of unordered key-value pairs. Each element in the dictionary is a combination of a key and a value, and the key value must be unique in the dictionary, so it is convenient to use the key from the dictionary to get the value of its corresponding value

The creation of a dictionary

Animals = {1: ' Tiger ', 2: ' Lion ', 3: ' Horse '}

ANIMALS[1]

' Tiger '

The acquisition of value in a dictionary

If key does not exist, then Dict[key] throws an error, sometimes in order to avoid the error, we use the Get () function to obtain the value of the key, if the key does not exist, then the default returns None

Animals.get (1)

' Tiger '

Animals.get (4, ' default ')

' Default ' #key不存在的时候, return defaults

adding elements

Animals[4]= ' Eagle ' #只需要为字典中key进行赋值

Animals

{1: ' Tiger ', 2: ' Lion ', 3: ' Horse ', 4: ' Eagle '}

Delete Element

Del Animals[4]

Animals

{1: ' Tiger ', 2: ' Lion ', 3: ' Horse '}

Get keys and values

List (Animals.keys ())

[1,2,3]

List (Animals.values ())

[' Tiger ', ' lion ', ' horse ']

For Valuein animals.values ():

Print (value)

>

Tiger

Lion

Horse

Assignment and shallow copy and deep copy

col = [' Red ', ' blue ', ' green ']

Col_new =col

Col_new.append (' black ')

Col_new

[' Red ', ' blue ', ' green ', ' black ']

Col

[' Red ', ' blue ', ' green ', ' black '] #这个是赋值

Id_row =[id (ele) for Ele in Col]

Id_new =[id (ele) for ele in col_new] we can see the top two are the same

Here's a deep copy, you can look at it with a light cuff.

Importcopy

Col =[' Red ', ' blue ', ' green '

Col_new =copy.deepcopy (COL)

Col_new.append (' black ')

Col_new

[' Red ', ' blue ', ' green ', ' black ']

Col

[' Red ', ' blue ', ' green ']

We have to restudying, Python learning is to practice their own hands-on, more code to knock.