Python04 Create list of list characteristics of list get the index of the specified element get a single element in the list get multiple elements in the list -- Slicing operation list element querying operation list element adding operation list element deleting operation list element modifying operation list element sorting operation list generating formula
Why do I need a list
A variable can store an element , And the list is a “ Big container ” Can be stored n Multiple elements , The program can easily operate the data as a whole
Lists are equivalent to arrays in other languages
# Flow control statement ：break And continue Use in double cycle for i in range(5): # Represents the outer loop execution 5 Time for j in range(1,11): if j % 2 == 0: continue print(j, end='\t') print()
Use brackets
Call built-in functions list（）
''' The first way to create a list , Use brackets ''' lst = ['hello', 'world', 98] ''' The second way to create a list , Use built-in functions list（）''' lst2 = list(['hello', 'world', 98])
The list elements are sorted in order
Index maps the only data
Lists can store duplicate data
Mixed storage of any data type
Dynamically allocate and reclaim memory as needed
''' The first way to create a list , Use brackets ''' lst = ['hello', 'world', 98, 'hello'] print(lst) print(lst[0], lst[-4]) ''' The second way to create a list , Use built-in functions list（）''' lst2 = list(['hello', 'world', 98])
If there are multiple identical elements in the list , Only the index of the first element of the same element in the list is returned
If the element of the query does not exist in the list , It will appear ValueError
It can also be in the specified start and stop Search between
lst = ['hello', 'world', 98, 'hello']
print(lst.index('hello'))
# print(lst.index('Python')) # ValueError: 'Python' is not in list
# print(lst.index('hello', 1, 3)) # ValueError: 'hello' is not in list
print(lst.index('hello', 1, 4)) # 3Forward index from 0 ~ n-1
Reverse index from -n ~ -1
The specified index does not exist , when indexError
lst = ['hello', 'world', 98, 'hello', 'world', 234] # Get the index as 2 The elements of print(lst[2]) # Get the index as -3 The elements of print(lst[-3]) # Get the index as 10 The elements of # print(lst[10]) # IndexError: list index out of range
Grammar format ： List name 【start：stop：step】
step When it's negative ： The first element of the slice defaults to the last element of the list ; The last element of the slice defaults to the first element of the list
lst = [10, 20, 30, 40, 50, 60, 70, 80]
# start = 1, stop = 6, step = 1
# print(lst[1:6:1]) # [20, 30, 40, 50, 60]
print(" Original list ：", id(lst))
lst2 = lst[1:6:1]
print(" Cut segment ：", id(lst2))
print(lst[1:6]) # [20, 30, 40, 50, 60] # The default step size is 1
print('------------step When the step size is positive -----------')
print(lst[1:6:]) # The default step size is 1
# start = 1, stop = 6, step = 2
print(lst[1:6:2]) # [20, 40, 60]
# start By default , stop = 6, step = 2
print(lst[:6:2]) # [10, 30, 50]
# start 1, stop By default , step = 2
print(lst[1::2]) # [20, 40, 60, 80]
print('------------step When the step size is negative -----------')
print(' Original list ：', lst)
print(lst[::-1]) # Output the list elements in reverse order [80, 70, 60, 50, 40, 30, 20, 10]
# start 7, stop Omit , step = -1
print(lst[7::-1]) # [80, 70, 60, 50, 40, 30, 20, 10]
# start 6, stop 0, step = -2
print(lst[6:0:-2]) # [70, 50, 30]Determine whether the specified element exists
print('p' in 'python') # True
print('k' not in 'python') # True
lst = [10, 20, 'python', 'hello']
print(10 in lst) # True
print(100 in lst) # False
print(10 not in lst) # False
print(100 not in lst) # TrueTraversal of list elements
lst = [10, 20, 'python', 'hello'] for item in lst: print(item)
append（）： Add an element at the end of the list
extend（）： Add at least one element at the end of the list
insert（）： Add an element anywhere in the list
section ： Add at least one element anywhere in the list
# Add an element to the end of the list
lst = [10, 20, 30]
print(' Before adding ：', lst)
print(id(lst))
lst.append(100)
print(' After adding ：', lst)
print(id(lst))
lst2 = ['hello', 'world']
# lst.append(lst2) # take lst2 Add to the end of the list as an element
# print(lst) # [10, 20, 30, 100, ['hello', 'world']]
lst.extend(lst2) # Add more than one element at a time to the end of the list
print(lst) # [10, 20, 30, 100, 'hello', 'world']
lst.insert(1, 90) # Add an element anywhere
print(lst) # [10, 90, 20, 30, 100, 'hello', 'world']
lst3 = [True, False, 'hello']
# Add... Anywhere n Multiple elements
lst[1:] = lst3
print(lst) # [10, True, False, 'hello']remove（）： Delete one element at a time ; Duplicate elements delete only one , There is no element explosion ValueError
pop（）： Deletes an element at a specified index position ; If the specified element does not exist, it will be exploded IndexError; Do not specify element bits , Then delete the last element in the list
section ： Delete at least one element at a time , Slicing produces a new list object
clear（）： Clear the list
del： Delete list
lst = [10, 20, 30, 40, 50, 60, 30]
lst.remove(30) # Remove an element from the list , If there are repeating elements , Remove only the first element
print(lst) # [10, 20, 40, 50, 60, 30]
# lst.remove(100) # ValueError: list.remove(x): x not in list
# pop（） Remove elements according to index
lst.pop(1)
print(lst) # [10, 40, 50, 60, 30]
# lst.pop(5) # IndexError: pop index out of range If the specified index location does not exist , Throw an exception
lst.pop() # If no parameters are specified （ Indexes ）, The last element of the list will be deleted
print(lst)
print('--------------- Slicing operation - Delete at least one element , A new list object will be generated -----------------')
new_list = lst[1:3]
print(' Original list ：',new_list) # Original list ： [40, 50]
''' No new list objects are generated , Instead, delete the contents of the original list '''
lst[1:3] =[]
print(lst) # [10, 60]
''' Know all the elements in the list '''
lst.clear()
print(lst) # []
'''del Statement to delete a list object '''
del lst
# print(lst) # NameError: name 'lst' is not definedAssign a new value to the element of the specified index
Assign a new value to the specified slice
lst = [10, 20, 30, 40] # Modify one value at a time lst[2] = 100 print(lst) # [10, 20, 100, 40] lst[1:3] = [300, 400, 500, 600] print(lst) # [10, 300, 400, 500, 600, 40]
call sort（） Method , By default, all elements in the list are sorted from small to large , You can specify reverse = True, Sort in descending order
Call built-in functions sorted（）. You can specify reverse = True, Sort in descending order , The original list doesn't change
lst = [20, 40, 10, 98, 54]
print(' The list before sorting ', lst, id(lst))
# Start sorting , Call the of the list object sort Method , Default ascending order
lst.sort()
print(' Sorted list ', lst, id(lst)) # [10, 20, 40, 54, 98]
# By specifying keyword parameters , Sort the elements in the list in descending order
lst.sort(reverse=True) # reverse=True Represents a descending sort reverse=False Indicates ascending sort
print(lst) # [98, 54, 40, 20, 10]
lst.sort(reverse=False) # reverse=True Represents a descending sort reverse=False Indicates ascending sort
print(lst) # [10, 20, 40, 54, 98]
print('---------- Use built-in functions sorted（） Sort list , A new list object will be generated --')
lst = [20, 40, 10, 98, 54]
print(' The list before sorting ', lst) # The list before sorting [20, 40, 10, 98, 54]
# Start sorting
new_list = sorted(lst)
print(' Sorted list ', new_list) # Sorted list [10, 20, 40, 54, 98]
# Specify keyword parameters , Realize the descending sorting of list elements
desc_list = sorted(lst, reverse=True)
print(desc_list) # [98, 54, 40, 20, 10]abbreviation ： The formula for generating the list
Be careful ：“ Expressions that represent list elements ” It usually contains custom variables
lst = [i*i for i in range(1,10)] print(lst) # [1, 4, 9, 16, 25, 36, 49, 64, 81] ''' The elements in the list are 2,4,6,8,10''' lst2 = [2*i for i in range(1,6)] print(lst2) # [2, 4, 6, 8, 10]
