Python notes: List

yukiwu 2021-02-23 00:07:20
python notes list


Maybe like most ordinary people , I went through a special 2020 year . At sea , Getting sleepy , Straighten out self-cultivation .

finally 2021 In the spring of the recovery of all things , I stood myself up , Start learning and recording again . The first step is to organize or review systematically Python. I used to study intermittently because of my work , All the knowledge you know is scattered , Writing code is patchwork .

I hope this review can get a complete picture .

List

list Is the container data type (collection) One of them , It allows multiple values to be stored in a variable .

List Constants

list Can store any Python data type , for example number,string,character, Even list.

list = [] #empty list
list = [1, 2, 3, 4]
list = ['a', 'b', 'c', 'd']
list = ["apple", "banana", "cat", "dog"]
list = [1, [2, 3], 4]

And string similar ,list You can also use indexing obtain list A value in , Such as :

list = [1, 2, 3, 4]
print(list[2])
>> 3

But and string The difference is , list The value of is modifiable , and string The value of is not modifiable .

list = ['a', 'p', 'p', 'l', 'e']
list[2] = 'x'
print(list)
>> ['a', 'p', 'x', 'l', 'e']

List Manipulating

To connect or divide list, There are two important symbols , Namely “+” and “:”.

“+” It's used to connect two list, Such as :

a = [1, 2]
b = [3, 4]
list = a + b
print(list)
>> [1, 2, 3, 4]

“:” It's for segmentation list Of , Such as :

list = [1, 2, 3, 4, 5]
sublist = list[1:3] #from index = 1 to index = 3-1
print(sublist)
>> [2, 3]
sublist = list[:3] #from index = 0 to index = 3-1
print(sublist)
>> [1, 2, 3]
sublist = list[1:] #from index = 1 to index = len(list) -1
print(sublist)
>> [2, 3, 4, 5]

List Methods

List a few commonly used methods.

  • append: Add a new value
  • in: Check list Whether to include a value
list = [1, 2, 3, 4]
print(9 in list)
>> False
  • sort: Yes list Sort by
  • len: Calculation list The length of
  • max,min,sum: Calculation list The maximum of , Minimum and sum

List and Loop

If you need to traverse list Each value in is also simple , We can use for:

list = [1, 2, 3, 4, 5]
for ii in list:
print(ii)

You can also use for and range() Traverse list Medium index, To obtain list Value :

list = [1, 2, 3, 4, 5]
for ii in range(len(list)):
print(list[ii])
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