Python basic variable type -- list analysis

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Python Use list

One 、list

Python One of the built-in data types is list ：list.list It's an orderly collection , You can add and remove elements at any time .

such as , List the names of all the students in the class , You can use one list Express ：

classmates = ['Michael', 'Bob', 'Tracy']
print(classmates)

Variable classmates It's just one. list.

len() function

1. get list Number of elements ：

classmates = ['Michael', 'Bob', 'Tracy']
print(len(classmates))

Visit with an index list Elements in every position in , Remember the index is from 0 At the beginning ：

classmates = ['Michael', 'Bob', 'Tracy']

print(classmates[0])

print(classmates[1])

print(classmates[2])

print(classmates[3])

When the index is out of range ,Python Will report a IndexError error , therefore , Make sure that the index doesn't cross the boundary , Remember that the index of the last element is len(classmates) - 1.

If you want to take the last element , Besides calculating the index position , You can also use -1 Do the index , Get the last element directly ：

print(classmates[-1])

And so on , You can get the last 2 individual 、 Last but not least 3 individual ：

classmates = ['Michael', 'Bob', 'Tracy']

print(classmates[-1])

print(classmates[-2])

print(classmates[-3])

print(classmates[-4])

Of course , Last but not least 4 It's just over the line .

2. list It's a variable ordered list , Go to list Add elements to the end of ：

classmates = ['Michael', 'Bob', 'Tracy']

classmates.append('Adam')

print(classmates)

You can also insert elements into the specified location , For example, the index number is 1 The location of ：

classmates = ['Michael', 'Bob', 'Tracy']
# Replace 
classmates.insert(1, 'Jack')

print(classmates)

pop() function

1. Delete list The element at the end

classmates = ['Michael', 'Bob', 'Tracy']

print(classmates.pop())

print( classmates)
['Michael', 'Jack', 'Bob', 'Tracy']

2. Deletes the element at the specified location , use pop(i) Method , among i It's the index position .

classmates.pop(1)

print(classmates)

3. Replace one element with another , It can be directly assigned to the corresponding index position ：

classmates = ['Michael', 'Bob', 'Tracy']

classmates[1] = 'Sarah'

print(classmates)

list The data types of the elements inside can also be different , such as ：

L = ['Apple', 123, True]

list The element can also be another list, such as ：

s = ['python', 'java', ['asp', 'php'], 'scheme']
print(len(s))

it is to be noted that s Only 4 Elements , among s[2] Another list, It's easier to understand if you take it apart ：

p = ['asp', 'php']
s = ['python', 'java', p, 'scheme']

To get 'php' Can write p[1] perhaps s[2][1], therefore s It can be seen as a two-dimensional array , There's a similar three-dimensional 、 4 d …… Array , But it's rarely used .

If one list None of the elements in , It's just an empty list, Its length is 0：

L = []
len(L)

Two 、 summary

This article is based on Python Basics , It mainly introduces Python In the foundation list list , adopt list Two functions of the list , Yes list The grammar is explained in detail , With a wealth of cases , The display of the code effect diagram helps you to better understand .

Use Python programing language , It is convenient for us to understand , I hope it will help you in your study . Want to learn more Python Web crawler and data mining knowledge , Go to a professional website ：http://pdcfighting.com/ Want to learn more Python Web crawler and data mining knowledge , Go to a professional website ：http://pdcfighting.com/