Python notes 03 List Dictionary

1.for,while Loop traversal

2. Adding elements

Append

You can add elements to a list by append

    #定义变量A，默认有3个元素    A = [‘xiaoWang‘,‘xiaoZhang‘,‘xiaoHua‘]    print("-----添加之前，列表A的数据-----") for tempName in A: print(tempName) #提示、并添加元素 temp = input(‘请输入要添加的学生姓名:‘) A.append(temp) print("-----添加之后，列表A的数据-----") for tempName in A: print(tempName)

Results:

Extend

By extend you can add elements from another collection to the list one by one

>>> a = [1, 2]>>> b = [3, 4]>>> a.append(b)>>> a[1, 2, [3, 4]]>>> a.extend(b)>>> a[1, 2, [3, 4], 3, 4]

Insert

Insert (Index, object) inserts an element in the specified position before Index object

>>> a = [0, 1, 2]>>> a.insert(1, 3)>>> a[0, 3, 1, 2]

Del: Delete del xx "0" according to the subscript

Pop: Delete the last element Xx.pop

Remove: Delete Xx.remove (') based on the value of the element

The sort method is to rearrange the list in a specific order, by default, from small to large, and the parameter reverse=true can be changed to reverse, from large to small.

The reverse method is to reverse the list.

Xx.sort ()

Xx.reverse ()

Meta-group

A python tuple is similar to a list, except that the elements of a tuple cannot be modified . tuples use parentheses, and the list uses square brackets.

Dictionary key key value

Note that in the dictionary operation, the dictionary is judged by the key

modifying elements

The data in each element of the dictionary can be modified, as long as it is found by key and can be modified

Demo

    info = {‘name‘:‘班长‘, ‘id‘:100, ‘sex‘:‘f‘, ‘address‘:‘地球亚洲中国北京‘} newId = input(‘请输入新的学号‘) info[‘id‘] = int(newId) print(‘修改之后的id为%d:‘%info[‘id‘])

If the "key" in the dictionary does not exist when using the variable name [' key '] = Data , then this element will be added

Delete Element

To delete a dictionary, there are a few things:

• Del Delete
• Clear () Clear

<1>len ()

Number of key-value pairs in the measurement dictionary

<2>keys

Returns a list containing all keys for the dictionary

<3>values

Returns a list containing all the value of the dictionary

<4>items

Returns a list containing all (key, value) Ganso

<5>has_key

Dict.has_key (Key) returns True if key is in the dictionary, otherwise false

Dictionary traversal

For key in XXXX

For value in XXXX

For item in XXXX element

For Key,value in XXXX key value pair

Enumerate () use

• If you want to traverse the index and iterate through the elements on a list, you can first write this:

list1 = ["这", "是", "一个", "测试"]for i in range (len(list1)): print i ,list1[i]

• The above method is somewhat cumbersome, and the use of enumerate () will be more direct and graceful:

list1 = ["这", "是", "一个", "测试"]for index, item in enumerate(list1): print index, item>>>0 这1 是2 一个3 测试

• Enumerate can also receive a second parameter that specifies the index starting value, such as:

list1 = ["这", "是", "一个", "测试"]for index, item in enumerate(list1, 1): print index, item>>>1 这2 是3 一个4 测试

CMP (ITEM1, ITEM2) compares two values

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Python notes 03 List Dictionary