Python Learning Notes
python language base
variable
Variable name specification:
1. Can only consist of letters, numbers and underscores
2. Cannot start with a number
3. You cannot name a Python built-in key
data type
int plastic float float str Character string bool Boolean tuple tuple list list set aggregate dict Dictionaries
Format
%s Format output string %f Format Output Floating Point %d Formatted output signed decimal integer
input
input() Enter information that accepts input from the user
Syntax: input
Characteristic:
- The console freezes when it encounters an input and waits for the user to enter information before the program continues to run
- input inputs are generally assigned to variables
eval Data type for extracting variable values a='0.1' eval(a) After running a It is no longer a character type. And it's floating point
Grammatical Structure
Single Branch Selection Structure
Grammar:
if condition:
Conditional True False
Execute Statement
Be careful with indentation!!!
age = 13
if age > 18:
# Only if the if condition is met will the following three output statements be output; if not, only the last output statement will be output
print("You're an adult,Can go online")
print("Welcome")
# A single output statement that does not involve the if statement will output regardless of whether the if condition is met
print("You are not old enough")
Double Branch Selection Structure
if conditional expression:
Code Block 1
else:
Code Block 2
age = int(input("Please enter your age:"))
if age > 18:
print(f"Your age is{age}year,You're an adult")
print("Welcome")
else:
print(f"Your age is{age},You are still under age")
print("Contact the network administrator if you want to go online")
print("System shutdown~")
Multi-Branch Selection Structure
if (conditional expression 1):
Code Block 1
elif (conditional expression 2):
Code Block 2
Else (conditional expression 3):
Code Block 3
grade = eval(input("Please enter your score:\n"))
if 100 >= grade >= 60:
print(f"Your results are{grade},Passed")
print("Reward a chocolate")
elif grade >= 0:
print(f"Your results are{grade},Your grades failed")
print("Take the bucket to the factory")
else:
print("You're a bad boy")
for loop
for loop variable in range():
Circulatory body
for i in range(0, 10, 2):
# 0 is the initial value, can not be written, the default value is 0.10 is the end value, but the output does not include 10, 2 is the number of steps, just like I walk two numbers in one step, is the multiple of 2
print(i)
b = 0;
for i in range(101): # range takes an integer
if i % 2 == 0:
b += i
print(f"1~100 Even sum of{b}")
break and continue
break jumps out of the loop and ends the whole cycle
continue Jumps Out of this Loop to continue the Next Loop
for i in range(1, 6):
if i == 3:
# break # Output to end of 3 loop
continue # Skip number 3 to continue next cycle
print(i)
while else and for else
for ... else:
A statement within an else is a statement executed after the normal end of the loop
If the loop ends with a brake, statements within an else will no longer be executed
while ... else:
A statement within an else is a statement executed after the normal end of the loop
If the loop ends with a brake, statements within an else will no longer be executed
for i in range(1, 5):
print(i)
else:
print("End of cycle") # The normal end of the loop will run the contents of else
print("Hey Hey")
data structure
Initial string
Define a single-line string '' "" ''' ''' """ """ Define a multiline string \n \t Normal output
Index and slicing of strings
str1 = 'abcdefg' # Subscript is also called index numbering from 0 # Format: [Subscript] Subscript can be positive or negative print(str1[0]) # a print(str1[-4]) # d # Slice [Start subscript (inclusive): End subscript (excluded): Step] print(str1[0:3:1]) # abc print(str1[0:3:2]) # ac print(str1[0:3]) # Step size can be saved by default to 1 print(str1[:3]) # Start subscript can be omitted, default start from 0 print(str1[1:]) # End subscript can also be omitted, default to end print(str1[::-1]) # str1[::-1] Reverse output # String is an immutable operation that cannot be added or deleted
List
'''
Currency conversion: Renminbi￥And US Dollars $Conversion
The user enters the amount and currency symbols to be converted to￥or $End
Convert to Renminbi 6 if the user enters US dollars.382
If the user enters Renminbi, the converted rate is 0.1567
If no symbol is entered by the user, an error is prompted and re-entered
Keep two decimal places for the final result
'''
while True:
money = input('Please enter the amount and currency symbol to be converted to￥or $End:')
if money[-1] == '$':
USD = eval(money[0:-1])
money1 = USD * 6.382
print(f'The amount you entered is{USD}, The converted amount is{money1:.2f}')
break
elif money[-1] == '￥':
RMB = eval(money[0:-1])
money2 = RMB * 0.1567
print(f'The amount you entered is{RMB}, The converted amount is{money2:.2f}')
break
else:
print('The format you entered is incorrect, please re-enter!')
String additions and deletions
str1 = 'hello,python'
# find('substring', start subscript, end subscript) find subscript
# Find finds the first subscript, returns the first substring subscript, and cannot find the Return-1
# print(str1.find('y')) # Find the subscript for y
# print(str1.find('o')) # Find the subscript for o and return the subscript for the first substring
# print(str1.find('o', 5, 11)) # Include at start and exclude at end
# print(str1.rfind('l')) # Search from right by default
# index() lookup
# index('substring', start subscript, end subscript) lookup
# print(str1.index('a')) # Return is the subscript of the first substring, no error found
# count() counts the number of substrings, returning 0 if none exist
# count('substring', start subscript, end subscript)
print(str1.count('y'))
String substitution
# replacer('old substring','New substring')
str1 = 'hello python'
# Replace python with world
str2 = str1.replace('python', 'world')
print(str1)
print(str2)
Method of String
# split('delimiter') splits a string into multiple objects
# Multiple objects stored in a list
'''
str1 = 'hello,python'
print(str1.split(','))
'''
# strip() removes symbols before and after strings, mostly to remove spaces
'''
str2 = '==hello=='
print(str2)
print(str2.strip('')) # Remove whitespace
print(str2.strip('='))
print(str2.strip('=').strip(',')) # Remove left and right symbols
'''
# str.join(stp) is to add str to STP
# stp can be a string or a list
'''str3 = 'hello'
li1 = ['h', 'e', 'l', 'l', 'o']
print(','.join(str3))
print(''.join(li1))'''
# lower() all lowercase
'''str4 = 'JJHJHKJDSDSD'
print(str4.lower())'''
# upper() all converted to uppercase
'''str5 = 'adsddddfds'
print(str5.upper())'''
# title() initials uppercase
'''str6 = 'hello,python'
print(str6.title())'''
# Len (string name) Gets the length of the string
'''str7 = 'aaaaaaaaaaaaaaaaaaa'
print(len(str7))'''
# Max (string name) maximum by 26 letters
'''str8 = 'abcdefgABCDEFG'
print(max(str8))''' # g
# Min (string name) takes the minimum value
'''print(min(str8))''' # A
tuple
Initial tuple
tuple() Cast to tuple
Index and slicing of tuples
Tuple [subscript] can be positive or negative
Slice [Start: End: Step] Contains Start but does not Contain End
A tuple is an immutable data type, but if a variable data type such as a list is placed inside the tuple, the data in the list can be changed.
Tuple lookup
index() returns the subscript of the first matching element that cannot be found and will cause an error
count() returns the number of matching elements
list
Initial list
Definition List Lists can hold all data types Define an empty list [] list() Two forms of defining empty lists Define a list with data [Data 1, Data 2, data n] list(data) Two lists with data defined list() Convert other types to lists
len() returns the length of the list
max() returns the maximum value
min() returns the minimum value
Index and Slice of List
Subscript, assign a subscript in order from 0
List name [subscript] subscript can be positive or negative
Lists are variable data types that can be added, deleted, altered, and checked
Increase in list
append() Append data to the end of the list Syntax: List name.append(data) extend() Append data to the end of the list insert(subscript, data) Insert data into a fixed location
List Lookup
index() Returns the subscript of the first data found count() Number of Statistics
Delete List
del delete Public method deletes all data types del Variable Name del List Name[subscript] Remove fixed subscript elements
pop() delete List Name.pop(subscript) Remove the fixed subscript element and return its value pop()Delete the last element if no subscript is written
remove() Delete Remove Matching First Element
sort() Sorted, default from smallest to largest reverse=False Default value from small to large reverse() Reverse Output
Dictionaries
Initial Dictionary
dict Dictionaries
{key1:value1, key2:value2}
key Value is unique if key Repeat, output last
{} Define an empty dictionary
dict() Factory function dict Create an empty dictionary
dict()Created with key-value Dictionaries key Cannot quote
zip() Merge multiple data to merge with the fewest elements
fromkeys(keys,value) If value Omit, enter none Define a dictionary key Different, value Same dictionary
New Dictionary
# Dictionaries are variable data types
dict1 = {'name': 'Ada', 'age': 20}
'''
print(dict1[0]) # Dictionaries do not support subscripts and slicing
print(dict1['name']) # You can use key to return value
'''
# Dictionary name [key] = value adds a key-value
'''
dict1['name'] = 'Afei' # Modify the value if the key exists
dict1['height'] = '183cm' # If key does not exist, add a key-value
print(dict1)
'''
# Dictionary name. update() adds more than one key-value
'''
dict2 = {'width': 140, 'hobby': 'Play with the smarthphone'}
dict1.update(dict2)
print(dict1)
'''
# Set default (key, value) add a key-value
'''
dict1.setdefault('girlfriend', 'lili') # If key does not exist, add a key-value
dict1.setdefault('width', '150') # Value value cannot be modified if key exists
print(dict1)
'''
Delete Dictionary
del Dictionary Name Deletes the entire dictionary Dictionary Name.pop(key) delete key-value，And back value popitem() Delete Last key-value clear() Empty Dictionary
Dictionary Lookup
Dictionary Name[key] Return this key Of value Dictionary Name.get(key) Return this key Of value keys() Return to All key values() Return to All value items() Return to All key-value
aggregate
Initial Set
set{Element 1, element 2, element n}
Collection has automatic weighting
{}Define an empty dictionary, not an empty collection
set()Force Conversion to Collection
The collection is out of order and cannot be indexed(subscript)And slicing,It cannot be connected, checked or counted.
Delete and increase of collection
add() Add one data at a time update() Add multiple new data, which can be lists, tuples, collections pop() delete remove() Delete Delete Fixed Values sorted() Sort from smallest to largest by default copy() copy
Student Management System
student = []
# str.center(40,'*') centering text makes str 40, insufficient complement*
print('Welcome to the Student Management System'.center(30, '='))
while True:
print('''Please enter the serial number to select the appropriate function:
1,Add Student Information
2,Delete Student Information
3,Modify Student Information
4,Query Student Information
5,Query all students
6,Exit the current system''')
num = input('Enter the serial number for the function:')
if num == '1': # Add Student Information
'''
1.Student Information: Class 100, Age 21, School Number 1000, Gender, Name
Student information is stored in a dictionary
2.Determine if a number exists: it is unique
If the number exists: the student's information cannot be added
If the number does not exist, append the student information to student List append()
'''
print('New Student Information Interface'.center(30, '-'))
new_class = input('Please enter the student's class:')
new_age = input('Please enter the student's age:')
new_id = input('Please enter the student's number:')
new_name = input('Please enter the name of the student:')
stu_dict = {} # Empty Dictionary Receives Student Information
for i in student:
if new_id == i.get('id'):
print('Student already exists')
else:
stu_dict['class'] = new_class
stu_dict['age'] = new_age
stu_dict['id'] = new_id
stu_dict['name'] = new_name
student.append(stu_dict)
print(student)
elif num == '2':
'''
Needs Analysis:
1.Delete by number
2.Delete the student if the number exists
3.If the number does not exist, it cannot be deleted
'''
print('Delete Student Information Interface'.center(30, '-'))
del_id = input('Please enter the student number you want to delete:')
# for...else
#
for i in student:
if del_id == i['id']:
student.remove(i)
break
else:
print('The number does not exist, please confirm before deleting')
print(student)
elif num == '3':
print('Modify Student Information'.center(30, '*'))
"""
Modify student information according to number:
1.Enter a number
2.Determine if the number exists 2-1 Exist, modify information 2-2 does not exist, no such person found
"""
modify_id = input('Please enter the student number that needs to be modified:')
for i in student:
if modify_id == i.get('id'):
i['class'] = input('Please enter a new class:')
i['age'] = input('Please enter a new age:')
i['name'] = input('Please enter a new name:')
break
else:
print('No such person found')
elif num == '4':
print('Query Student Information'.center(30, '*'))
query_id = input('Enter the number of the student you want to inquire about:')
for i in student:
if query_id == i['id']:
print(f'Class is{i["class"]}, The number is{i["id"]}, Age is{i["age"]}, Name is{i["age"]}')
break
else:
print('No such person found')
elif num == '5':
print('Query all students'.center(30, '*'))
print('class\t Age\t School Number\t Full name')
for i in student:
print(i["class"], i["age"], i['id'], i['name'])
elif num == '6':
ty = input('Whether to exit the current system(input y or n): ')
if ty == 'y':
break # break ends the entire loop
else:
continue # continue Ends the current loop and proceeds to the next one
else:
print('Error entering serial number, please re-enter:')
Derivation (Generation)
# Derivative (Generative) Simplified Code
# Syntax: variable for variable in range
# List derivation [variable for variable in range]
# [0，1，2，3，4，5，6，7，8，9]
li1 = []
for i in range(10):
li1.append(i)
print(li1)
li2 = [i for i in range(10)]
print(li2)
li3 = [1, 2, 1.1, 'a', 20.4, 'jj', 8]
# [variable for variable in range if condition]
li4 = [i for i in li3 if type(i) == int]
print(li4)
str1 = 'ABC'
str2 = '123'
print([i+j for i in str1 for j in str2])
# Dictionary derivation {key:value}
print({i: j for i in str1 for j in str2})
# Generate a dictionary with keys 1, 2, 3, 4, 5 being their squares
print({i: i**2 for i in range(1, 6)})
# Set derivation {}
l1 = [1, 2, 3, 1, 2, 3, 4, 5, 6]
# Place the square of each element in l1 in the set
print({i**2 for i in l1}) # Sets are out of order and automatically de-weighted
function
Definition and use of functions
Functions are designed to achieve more efficient code reuse and improve code consistency
Definition of function:
def Function name(parameter list):
"""Description Documentation(Notes)Usually on the first line"""
Function Body(Code)
Call function: Function name(parameter)
Notes: 1. Parameters may or may not be available for different requirements
2,stay python In, functions must be defined before they can be used
3,Functions must be called before they can be used
Parameters of the function
Parameters of a function: To make a function more flexible Parameters: When defining a function, parameters to end the data are also defined Arguments: The actual data passed when the function is called
Return value of function
return Returns a value, returning a value to the place where the function was called return: 1. Without return，Will return a None 2. return Represents the end of the current function, return The statement below will not be executed 3. If you want to return more than one value, go directly to the return Write multiple values, which are returned as tuples to the object calling the function 4. The return value can be of any data type 5. The return value can be assigned to a variable or passed to the next function as an argument
Parameter Advancement of Functions
# Position parameter transfers parameter position and number are fixed according to parameter position
def test01(name, age, sex):
print(f'Name is{name}，Age is{age}Age, gender{sex}')
test01('Conger', 1, 'Unknown')
# Keyword parameters are passed as "key = value"
test01(name='Agam', age=21, sex='male')
test01(age=21, sex='male', name='Agam') # The order of the parameters does not affect the output results and is more flexible than position parameters
# Default parameters, default parameters can pass parameters without passing arguments Default parameters must be at the end of the parameter list
def test02(name, age, sex='male'):
print(f'Name is{name}，Age is{age}，Gender is{sex}')
test02('Ada', 19)
test02('Asa', 28, 'female')
# Indefinite length parameter (indeterminate length)
# 1. Parcel location parameter * args passes parameters as tuples
def test03(*args): # test03(*aaa) parameter name is arbitrary
sum = 0
for i in args:
#sum = sum + i
sum += i
print(sum)
test03(10, 34, 45, 76, 99)
test03(100, 999999)
def test04(a, b, *args):
print(args, a, b)
test04(1, 2, 3, 4, 5, 6, 7)
# 2. Package keyword parameters**kwargs
def test05(**kwargs):
for i in kwargs:
print(i)
test05(name='Acar', age=19, sex='male')
# Define a function. Maximum and Minimum in Output List
def test06(*args):
args = list(args)
a = max(args)
b = min(args)
print(f"The maximum number you enter is{a},The minimum value is{b}")
Variable Scope of Function
# Variable Scope: The area in which the variable acts
# Local variable: A variable defined within a function whose area of action is within the function. Once the function is executed, the variable is destroyed
def test01():
a = 10
print(a)
test01()
# print(a) # A is a local variable and calls outside of functions will fail
# Global variables: variables that are available both inside and outside the function
b = 3
def test02():
global b # Declare b as a global variable
b = 10
print(id(b))
print(b)
test02()
print(f'The value of the global variable is{b}')
print(id(b))
# Local variables are faster than global variables and can be used optimally during use.
# Testing local and global variables
# import math as m # Name math m
import math
import time
qj = math.sqrt
def quanju():
start = time.time()
for i in range(10000000):
qj(199)
end = time.time()
print(f'Execution time of global variables{end-start}')
def jubu():
jb = math.sqrt
start = time.time()
for i in range(10000000):
jb(199)
end = time.time()
print(f'Execution time of local variable{end-start}')
quanju()
jubu()