Loop traversal of lists

1. Use the for loop

To output each data of the list more efficiently, you can use loops to complete it

demo:

    namesList = ['xiaoWang','xiaoZhang','xiaoHua']
    for name in namesList:
        print(name)

Result:

    xiaoWang
    xiaoZhang
    xiaoHua

2. Use the while loop

To output each data of the list more efficiently, you can use loops to complete it

demo:

    namesList = ['xiaoWang','xiaoZhang','xiaoHua']

    length = len(namesList)

    i = 0

    while i<length:
        print(namesList[i])
        i+=1

Result:

    xiaoWang
    xiaoZhang
    xiaoHua

List related operations

The data stored in the list can be modified, such as "add", "delete", "change".“

<1> Add elements ("add" append, extend, insert)

append

append lets you add elements to a list

demo:

    #Define variable A with three elements by default
    A = ['xiaoWang','xiaoZhang','xiaoHua']

    print("-----Before adding, list A Data-----")
    for tempName in A:
        print(tempName)

    #Prompt and add elements
    temp = input('Please enter the name of the student you want to add.:')
    A.append(temp)

    print("-----After adding, the list A Data-----")
    for tempName in A:
        print(tempName)

Results:

extend

You can add elements from another collection to the list one by one through extension

>>> 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 the element object before the specified position index

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

<2> Modify Elements ("Modify")

When modifying an element, the subscript is used to determine which element to modify before making the modification.

demo:

    #Define variable A with three elements by default
    A = ['xiaoWang','xiaoZhang','xiaoHua']

    print("-----Before modification, list A Data-----")
    for tempName in A:
        print(tempName)

    #Modifying elements
    A[1] = 'xiaoLu'

    print("-----After modification, the list A Data-----")
    for tempName in A:
        print(tempName)

Result:

    -----Before modification, list A Data-----
    xiaoWang
    xiaoZhang
    xiaoHua
    -----After modification, the list A Data-----
    xiaoWang
    xiaoLu
    xiaoHua

<3> Find Elements ("Find" in, not in, index, count)

The so-called lookup is to see if a specified element exists.

in, not in

The common methods of searching in python are:

• in (exists), if it exists, then the result is true, otherwise it is false.
• not in, if not, then the result is true, otherwise false

demo

    #List to be found
    nameList = ['xiaoWang','xiaoZhang','xiaoHua']

    #Get the name the user is looking for
    findName = input('Please enter the name you want to find:')

    #Find out if it exists
    if findName in nameList:
        print('The same name was found in the dictionary.')
    else:
        print('Can't find')

Result 1: (Find)

Result 2: (Not found)

Explain:

index, count

index and count are used in the same way as in strings

>>> a = ['a', 'b', 'c', 'a', 'b']
>>> a.index('a', 1, 3) # Note that the left closed right open interval
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: 'a' is not in list
>>> a.index('a', 1, 4)
3
>>> a.count('b')
2
>>> a.count('d')
0

<4> Delete elements ("Delete" del, pop, remove)

Analogy in real life, if a classmate transferred, then the name of the student after this article should be deleted; in the development of this function is often used to delete.

The common deletion methods of list elements are:

• del: Delete by subscript
• pop: Delete the last element
• remove: Delete based on the value of the element

demo:(del)

    movieName = ['Pirates of the Caribbean','Hacker empire','First Blood','Lord of the rings','The Hobbit','Fast & Furious']

    print('------Before deleting------')
    for tempName in movieName:
        print(tempName)

    del movieName[2]

    print('------After deletion------')
    for tempName in movieName:
        print(tempName)

Result:

    Before deletion
    Pirates of the Caribbean
    Hacker empire
    First Blood
    Lord of the rings
    The Hobbit
    Fast & Furious
    After deletion
    Pirates of the Caribbean
    Hacker empire
    Lord of the rings
    The Hobbit
    Fast & Furious

demo:(pop)

    movieName = ['Pirates of the Caribbean','Hacker empire','First Blood','Lord of the rings','The Hobbit','Fast & Furious']

    print('------Before deleting------')
    for tempName in movieName:
        print(tempName)

    movieName.pop()

    print('------After deletion------')
    for tempName in movieName:
        print(tempName)

Result:

    Before deletion
    Pirates of the Caribbean
    Hacker empire
    First Blood
    Lord of the rings
    The Hobbit
    Fast & Furious
    After deletion
    Pirates of the Caribbean
    Hacker empire
    First Blood
    Lord of the rings
    The Hobbit

demo:(remove)

    movieName = ['Pirates of the Caribbean','Hacker empire','First Blood','Lord of the rings','The Hobbit','Fast & Furious']

    print('------Before deleting------')
    for tempName in movieName:
        print(tempName)

    movieName.remove('Lord of the rings')

    print('------After deletion------')
    for tempName in movieName:
        print(tempName)

Result:

    Before deletion
    Pirates of the Caribbean
    Hacker empire
    First Blood
    Lord of the rings
    The Hobbit
    Fast & Furious
    After deletion
    Pirates of the Caribbean
    Hacker empire
    First Blood
    The Hobbit
    Fast & Furious

Sort (reverse)

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

The reverse method is to invert the list.

>>> a = [1, 4, 2, 3]
>>> a
[1, 4, 2, 3]
>>> a.reverse()
>>> a
[3, 2, 4, 1]
>>> a.sort()
>>> a
[1, 2, 3, 4]
>>> a.sort(reverse=True)
>>> a
[4, 3, 2, 1]