Python list List

1. What is a list
1.1 As a type of sequence, a list is a collection of ordered elements.
1.2 List is the most commonly used built-in data type in Python. It is enclosed in square brackets [Element 1, Element 2...] and separated by commas. There is no relationship between the elements and can be of any type.

2. List declaration and access

#!/usr/bin/python# -*- coding:utf-8 -*- #变量的声明market = ['Apple','Banana','computer']#打印列表元素print market[0],market[1],market[2],market[-1].title()#For循环打印列表元素for element in market:print element,element.title()

3. Modification, addition and deletion of elements in the list
3.1 Modify list elements, list name + corresponding element Index

       #修改索引值为2，即第3个元素值   market[2] = 'Telephone'   print market   #打印结果:['Apple', 'Banana', 'Telephone']

　3.2 Add elements to the list. Python provides the append() and insert() methods. append() means adding elements to the end of the list, and insert() can specify the list. Add elements at the position, such as:

       market.append('Orange')       print market  #得到结果:['Apple', 'Banana', 'computer', 'Orange']   market.insert(1,'Watermelon')       print market  #得到结果:['Apple', 'Watermelon', 'Banana', 'computer', 'Orange']

3.3 To delete elements from the list, you can use the del statement, pop() and remove() methods, such as:

       #删除第1个元素Apple   del market[0]       print market       #pop()方法删除列表末尾元素，可以接着使用它赋给其它的列表，如：   pop_market = market.pop() #此时把通过pop()方法弹出的末尾元素赋给新的变量pop_market   print type(pop_market) #通过打印pop_market的类型得知，此时类型为String <type>   #如果想让弹出的元素赋值给新的列表该怎么办呢，可以先声明列表，然后直接用 append()方法追加，如下:   pop_list_p = []
       pop_list_p.append(market.pop())       print pop_list_p       #或列表的切片，后续会提到   pop_list = market[-1]       print market       print pop_market       print pop_list       #remove()方法从列表中删除元素时，也可以接着使用它的值：   #使用remove()方法时，只需要制定元素对应的值即可，如：删除元素Watermelon   market.remove('Watermelon')       print market</type>

4. The organization of the list, the sort() method represents permanent sorting, the sorted() function represents temporary sorting, the reverse() method represents reversing the order of the list elements, len() The function represents the length of the list

market = ['Computer','Banana','Apple']
market.sort()print market #sort()方法永久性改变了列表的元素排列的顺序，结果：['Apple', 'Banana', 'Computer']#sorted()函数临时性改变了列表的元素排列的顺序market = ['Computer','Banana','Apple']print (sorted(market)) #临时性排序['Apple', 'Banana', 'Computer']print market #再次打印还是预先的顺序['Computer', 'Banana', 'Apple']market.reverse()print market #reverse()方法反转列表元素的顺序#确定列表元素长度，也即是列表包含的元素个数，注意在用len()函数统计列表元素时是从1开始的print len(market)

Some common operations on the list:

Use subscript index to access the value in the list, you can also use the form of square brackets Intercept the characters as follows:

list1 = ['physics', 'chemistry', 1997, 2000]

list2 = [1, 2, 3, 4, 5, 6, 7 ]

print("list1[0]: ", list1[0])

print("list2[1: 5]: ", list2[1:5])

Output result

list1[0]: physics

list2[1:5] : [2, 3, 4, 5]

Update list

You can modify or update the data items in the list, or you can use append() method to add list items

list = ['physics', 'chemistry', 1997, 2000]

print("Value available at index 2: ")

print(list[2])

list[2] = 2001

print("New value available at index 2 : ")

print(list[2])

Output result:

Value available at index 2:

1997

New value available at index 2 :

2001

Delete list elements

Use the del statement to delete elements of the list

list1 = ['physics', 'chemistry', 1997, 2000]

print(list1)

del list1[2]

print("After deleting value at index 2 : ")

print(list1)

The above example output result:

['physics', 'chemistry', 1997, 2000]

After deleting value at index 2 :

['physics', 'chemistry', 2000]

Python list script operators

The operators for + and * on lists are similar to strings. The + sign is used for combined lists, and the * sign is used for repeated lists

len([1, 2, 3])

>>>3

[1, 2, 3] + [4, 5, 6]

>>>[1, 2, 3, 4, 5, 6]

['Hi!'] * 4

>>>['Hi!', 'Hi!', 'Hi!', 'Hi !']

3 in [1, 2, 3]

>>>True

for x in [1, 2, 3]:

print(x)

>>>123

Python list interception

Python's list interception and string operation types are as follows

L = ['spam', 'Spam', 'SPAM!' ]

L[2] #Read the third element in the list

>>>SPAM!

L[-2] #Read the second to last element in the list

>>>Spam

L[1:] #Intercept the list starting from the second element

>>>'Spam', 'SPAM!'

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