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Python Basic Grammar

Article directory

• Python Basic Grammar
• • List
  • • Introduction to List
    • Slicing
    • List modification elements
    • List method
    • Loop through the list
  • sequence
  • • Basic operation of sequence
  • range() function
  • EMS (Employee Manager System) Exercise
  • tuple
  • Variable objects
  • Dictionary (dict)
  • • Loop through dictionary
  • Set
  • • Creation of collections
    • Operation of sets

List

- A list is an object in Python
 - An object is an area in memory dedicated to storing data
 - The object we learned before, like a value, it can only hold a single data
 - Multiple ordered data can be saved in the list
 - A list is an object used to store objects
 - Use of lists:
     1. List creation
     2. Manipulate the data in the list
 

Introduction to lists

# Create a list, use [] to create a list
 my_list = [] # creates an empty list
 # print(my_list, type(my_list))

 # The data stored in the list, we call it an element
 # Multiple elements can be stored in a list, or you can specify the elements in the list when creating the list
 my_list = [10] # create a list with only one element

 # When adding multiple elements to the list, use between multiple elements, separated
 my_list = [10,20,30,40,50] # Creates a protected list with 5 elements

 # Any object can be saved in the list
 my_list = [10,'hello',True,None,[1,2,3],print]

 # The objects in the list will be stored in the list in the order of insertion,
 # The first inserted object is saved to the first position, the second is saved to the second position
 # We can get the elements in the list by index (index)
 # The index is the position of the element in the list, each element in the list has an index
 # The index is an integer starting from 0, the first position index of the list is 0, the second position index is 1, the third position index is 2, and so on
 my_list = [10,20,30,40,50]

 # Get the elements in the list by index
 # Syntax: my_list[index] my_list[0]
 # print(my_list[4])
 # If the index used exceeds the maximum range, an exception will be thrown
 # print(my_list[5]) IndexError: list index out of range

 # Get the length of the list, the number of elements in the list
 # len() function, through which the length of the list can be obtained
 # The value of the obtained length is the maximum index of the list + 1
 print(len(my_list)) # 5
 

Slice

# slice
 # Slicing means getting a sublist from an existing list
 # Create a list, generally when creating a list, the name of the variable will use plural
 stus = ['Monkey King','Zhu Bajie','Monk Sand','Tang Monk','Spider Demon','Bone Demon']

 # List indices can be negative
 # If the index is a negative number, get the element from the back to the front, -1 means the first from the bottom, -2 means the second to the last, and so on
 # print(stus[-2])

 # Get the specified element by slicing
 # Syntax: list[start:end]
 # When getting elements by slice, the element at the start position will be included, and the element at the end position will not be included
 # When doing slice operations, a new list will always be returned without affecting the original list
 # The index of the start and end positions can be omitted
 # If the end position is omitted, it will be intercepted until the end
 # If the starting position is omitted, it will be intercepted from the first element
 # If the start position and end position are all omitted, it is equivalent to creating a copy of the list
 # print(stus[1:])
 # print(stus[:3])
 # print(stus[:])
 # print(stus)

 # Syntax: list[start:end:step]
 # The step size indicates the interval between getting elements each time, the default value is 1
 # print(stus[0:5:3])
 # The step size cannot be 0, but can be negative
 # print(stus[::0]) ValueError: slice step cannot be zero
 # If it is a negative number, elements will be taken from the back of the list to the front
 print(stus[::-1])


 

List modification element

# create a list
 stus = ['Monkey King','Zhu Bajie','Monk Sand','Tang Monk','Spider Demon','Bone Demon']

 # print("Before modification:", stus)
 # modify the elements in the list
 # Modify elements directly by index
 stus[0] = 'sunwukong'
 stus[2] = 'Haha'
 # Delete elements by del
 del stus[2] # delete index isAdd elements to the combination
 s.add(10)
 s.add(30)

 # update() adds an element in a collection to the current collection
 # update() can pass a sequence or dictionary as a parameter, and the dictionary will only use the key
 s2 = set('hello')
 s. update(s2)
 s. update((10,20,30,40,50))
 s.update({10:'ab',20:'bc',100:'cd',1000:'ef'})

 # {1, 2, 3, 100, 40, 'o', 10, 1000, 'a', 'h', 'b', 'l', 20, 50, 'e', ​​30}
 # pop() randomly deletes and returns an element in a collection
 # result = s. pop()

 # remove() deletes the specified element in the collection
 s. remove(100)
 s. remove(1000)

 # clear() clears the collection
 s. clear()

 # copy() makes a shallow copy of the collection

 #print(result)
 print(s, type(s))



 

Operation of sets

# When performing operations on a collection, the original collection will not be affected, but an operation result will be returned
 # Create two collections
 s = {1,2,3,4,5}
 s2 = {3,4,5,6,7}

 # & intersection operation
 result = s & s2 # {3, 4, 5}

 # | union operation
 result = s | s2 #{1,2,3,4,5,6,7}

 # - difference
 result = s - s2 # {1, 2}

 # ^ XOR set Get elements that only appear in one set
 result = s ^ s2 # {1, 2, 6, 7}

 # <= check if one set is a subset of another
 # If all the elements in set a appear in set b, then set a is a subset of set b, and set b is a superset of set a
 a = {1,2,3}
 b = {1,2,3,4,5}

 result = a <= b # True
 result = {1,2,3} <= {1,2,3} # True
 result = {1,2,3,4,5} <= {1,2,3} # False

 # < checks if a set is a proper subset of another set
 # If superset b contains all elements in subset a, and there are elements in b that are not in a, then b is a proper superset of a, and a is a proper subset of b
 result = {1,2,3} < {1,2,3} # False
 result = {1,2,3} = checks if one set is a superset of another
 # > Check if one set is a proper superset of another
 print('result =',result)