Python basics - list tuple

list tuple

Operators for list tuples

Use of len in list tuples

• The len function can calculate the length of all data types except numeric types

Accumulation and multiplication between lists (tuples)

• To add two lists you can use+
• Multiple accumulation of the same list can be used*

Usage of in and not in in lists (tuples)

• in is used to determine whether a member (element) is in the data structure
• not in is used to determine whether a member (element) is not in the data structure

append() function (adds an element to the current list)

• usage:

list.append(new_item)

• parameter

new_item:需要添加到列表中的元素

• Notice:
  • A new list will not be generated, it will be added to the original list
  • Elements being added will only be added to the end

insert() function (add an element to the specified position of the current list)

• usage:

list.insert(index,new_item)

• parameter

index:新元素的位置
new_item:需要添加到列表中的元素

• Notice:
  • append can only be added to the end of the list, insert can choose any position
  • If the index passed in by insert does not exist, a new element will be added to the end of the list
  • The positions of strings, tuples, and list elements are counted from 0

count() function (returns the number of a member in the current list) (tuples are available)

• usage:

inttype = list.count(item)

• parameter

item:需要查询个数的元素

• Notice:
  • Returns 0 if the queried member (element) does not exist
  • Using this function, only complete elements in the list or tuple are checked for content that needs to be calculated:
    • For example, "watermelon" exists in the list
    • if coun("West")
    • then return 0

remove() function (delete an element in the list)

• usage:

list.remove(item)

• parameter

item:准备删除的列表元素

• Notice:
  • If the member specified to be deleted does not exist in the list, an error will be reported directly
  • If there are multiple elements to be deleted, the first element from left to right will be deleted
  • The remove function does not create a new list, but deletes it from the original list

python's built-in function del (delete completely)

• del can completely delete the variable
• usage:

del 变量名

• parameter

变量名:准备删变量

• Notice:
  • If the deleted variable is reapplied, an error will be reported (variable is not defined)

reverse() function (reverse the current list order)

• usage:

list.reverse()

• parameter

无参数

• Notice:
  • Make changes to the current list

sort() function (sort the current list according to certain rules)

• usage:

list.sort(cmp=NONE,key=NONE,reverse=False)

• parameter

cmp --- 可选参数,指定排序方案
key --- 参数比较
reverse --- 排序规则,reverse= True 降序,reverse = False 升序(默认)

• Notice:
  • By default, sort according to the order of the first letter of the string and the size of the number
  • It is necessary to ensure that the elements in the list are of the same type, otherwise they cannot be sorted and an error will be reported
  • If the order of the current list meets the requirements, no further sorting will be performed

clear() function (clear all data in the current list)

• usage:

list.clear()

• parameter

无需传参

• Notice:
  • There is no return value, it is to modify the existing list

copy() function (copy the current list to the same list)

• usage:

list.copy()

• parameter

无需传参

• Notice:

  • The content of the new list is the same as that of the old list, but the memory address pointed to is different, not the same list in essence

  • The variable assigned twice is the same as the original variable, and the memory address pointed to is also the same, essentially the same list

  • copy is a shallow copy (after a certain data in the list changes, it will be affected by each other)

    # coding:utf-8
    a = [[1,2,3],[4,5,6]]
    b = a.copy()
    print(b)
    b[0].append(4)
    print(a)
    print(b)
    

  • You can use copy.deepcopy(X) to make a deep copy (deep copy also copies the deep data, and the original data and new variables do not share data at all)

    # coding:utf-8
    import copy
    
    a = [[1,2,3],[4,5,6]]
    b = copy.deepcopy(a)
    print(b)
    b[0].append(4)
    print(a)
    print(b)
    

extend() function (import elements in other lists or tuples into the current list at one time)

• usage:

list.extend(iterable)

• parameter

iterable 代表列表或者元组,该函数无返回值

• Notice:
  • The incoming parameter needs to be an iterable element
  • The elements of the iterable will be imported into the list

List indexing and slicing

index

• strings, lists and tuples
• The position recorded from the left is the index
• The index is represented by numbers, starting from 0 from left to right
• The maximum index of strings, lists (tuples) is their length - 1

slice

• Indexing is accessing a single element, while slicing is accessing a range of elements
• Use the colon to find the two separate indexes in the square brackets[0:3]
• Slicing rules, after demarcating the range, the left contains the right does not contain
• The list obtained by slicing is not the original list
• You can use [::-1]the way to reverse the list
• You can use [-3:-1]the reverse way to get elements
• Slices can be obtained by setting the step size[起始元素:终止元素(不包含):步长]
• You can use [0:0]the way to generate an empty list

Index acquisition and modification

• usage:

list[index]

• parameter

index 代表一个在存在范围内的索引

• Notice:
  • Data modification can only be within the index range
  • Lists cannot add values ​​by adding new indexes
  • You can list.index(item)find the index value of the item element in the list by

pop() function (remove elements in the list according to the index)

• usage:

list.pop(index)

• parameter

index 代表一个在存在范围内的索引

• Notice:
  • Data modification can only be within the index range, if it does not exist, an error will be reported
  • The function removes the element at that index and returns

del() function (deletes a list or its index)

• usage:

del list[index]

• parameter

index 代表一个在存在范围内的索引

• Notice:
  • This function will directly delete the value at the specified index position in the list without return value
  • Report an error if index (index) does not exist

Specificity of indexing and slicing in tuples

• Tuples can get indexes and slice indexes like lists
• The usage of the tuple function index is exactly the same as that of the list
• It is not possible to modify and delete elements by modifying the index (tuples are immutable)

String indexing and retrieval

• Indexing of strings is similar to indexing of lists
• Each character in the string has an index position
• The rest of the rules are similar to list indexing
• Strings cannot be modified and deleted through indexes
• String cannot be modified

String find and index functions

• Both are used to get the index position of the element
• usage:

string.index(item)
string.find(item)

• parameter

item 希望查找索引位置的元素

• Notice:
  • find can not find the corresponding element position will return -1
  • If the index cannot find the position of the corresponding element, an error will be reported directly