[worth collecting] for Python beginners, sort out the common errors of beginners + Python Mini applet! (code attached)

Introduction

I don't know what the best programming language in the world is ？

But life is short , I use Python！

** Write code , Mistakes are inevitable ,** The key is how to quickly locate errors , solve bug. Error message , Sometimes it doesn't provide effective information , Especially new programming

hand , Often make some low-level mistakes , such as Incorrect indentation , Missing quotation marks , Incomplete parentheses etc. , Here are some code mistakes that novices often make , I hope you're just getting started

My classmates have a little help ~ In addition to summarizing the common mistakes of novice programming, some simple novice small projects will be attached for everyone to learn ！

Text

One 、 Novice programming error

1） Basic mistakes that novices often make

1. Missing colon ：

a=[1,2,3,4,5,6,7,8,9]
for i in range(0,len(a))
    for j in range(i+1,len(a)):
        if a[j]<a[i]:
            a[i],a[j]=a[j],a[i]
print(a)
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Error message ：# Grammar mistakes ： invalid syntax

​

2. Incorrect indentation

For class definitions 、 Function definition 、 Flow control statement 、 Exception handling statements, etc , The colon at the end of the line and the indent of the next line , Indicates the beginning of the next block of code , and

The end of the indentation indicates the end of the code block . Code with the same indentation is considered a block of code .

num = 2
if num < 5:
print(num)
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​

Error message ：# The indentation error ： Blocks that need to be indented

3. The symbol is Chinese

Like a colon 、 Brackets are Chinese symbols, etc .

for i in range(2,102)：
    print(i)
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​ Error message ：

4. Wrong data type

Common examples are : Splicing different types of data, etc .

name = 'xiaoming'
age = 16
print(name+age)
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​ Error message ：

5. Misspelling variable or function name

6. Use keywords as file names 、 Class name 、 Function name or variable name .

Class name 、 Function name or variable name , Out of commission Python Language keywords . file name , Cannot conflict with standard library .

Python3 The key words are ：

and, as, assert, break, class, continue, def, del, elif,else, except, False, finally, for, from, global, if, import, in, is, lambda,None, nonlocal, not, or, pass, raise, return, True, try, while, with, yield
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error ：

7."=" treat as “==” Use

"=" Is the assignment operator ,"==" Is equal to the comparison operation , Used as a conditional judgment .

error ：

correct ：

8. Missing parameter self

Initialization function , Examples of function , Instance variables require default parameters self.

9. Variable not defined

Error message ：

Two 、 Code checklist

Here is a simple code checklist , Hope to be a little helpful for novices in programming , Only for reference , You can also summarize your programming mistakes .

3、 ... and 、 Novice entry applet

These examples are very simple and practical , Very suitable for beginners to practice . You can also try according to the purpose and tips of the project , Build your own solutions , Improve the level of programming .

1. Stone scissors and paper games

The goal is ： Create a command line game , Players can play in stone 、 Choose between scissors and cloth , With computers PK. If the player wins , The score will

add to , Until the end of the game , The final score will be shown to the player .

Tips ： Receive player's choice , And compared with the choice of the computer . The computer's selection is randomly selected from the selection list . If the player gets

- , Increase 1 branch .

import random
choices = ["Rock", "Paper", "Scissors"]
computer = random.choice(choices)
player = False
cpu_score = 0
player_score = 0
while True:
    player = input("Rock, Paper or  Scissors?").capitalize()
    #  Judge the choice of players and computers 
    if player == computer:
        print("Tie!")
    elif player == "Rock":
        if computer == "Paper":
            print("You lose!", computer, "covers", player)
            cpu_score+=1
        else:
            print("You win!", player, "smashes", computer)
            player_score+=1
    elif player == "Paper":
        if computer == "Scissors":
            print("You lose!", computer, "cut", player)
            cpu_score+=1
        else:
            print("You win!", player, "covers", computer)
            player_score+=1
    elif player == "Scissors":
        if computer == "Rock":
            print("You lose...", computer, "smashes", player)
            cpu_score+=1
        else:
            print("You win!", player, "cut", computer)
            player_score+=1
    elif player=='E':
        print("Final Scores:")
        print(f"CPU:{cpu_score}")
        print(f"Plaer:{player_score}")
        break
    else:
        print("That's not a valid play. Check your spelling!")
    computer = random.choice(choices)
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2. Send Email automatically

​ Purpose ： Write a Python Script , You can use this script to send email .

Tips ：email Libraries can be used to send e-mail .

import smtplib 
from email.message import EmailMessage
email = EmailMessage() 
email['from'] = 'xyz name'   
email['to'] = 'xyz id'      
email['subject'] = 'xyz subject'  
email.set_content("Xyz content of email") 
with smtlib.SMTP(host='smtp.gmail.com',port=587)as smtp:     
## sending request to server 
    smtp.ehlo()        
smtp.starttls()    
smtp.login("email_id","Password") 
smtp.send_message(email)   
print("email send")   
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3.Hangman Little games

Purpose ： Create a simple command line hangman game .

Tips ： Create a list of password words and randomly select a word . Now underline each word “_” Express , Give users the chance to guess words , If the user guesses the right word , Will “_” Replace... With words .

import time
import random
name = input("What is your name? ")
print ("Hello, " + name, "Time to play hangman!")
time.sleep(1)
print ("Start guessing...\n")
time.sleep(0.5)
## A List Of Secret Words
words = ['python','programming','treasure','creative','medium','horror']
word = random.choice(words)
guesses = ''
turns = 5
while turns > 0:         
    failed = 0             
    for char in word:      
        if char in guesses:    
            print (char,end="")    
        else:
            print ("_",end=""),     
            failed += 1    
    if failed == 0:        
        print ("\nYou won") 
        break              
    guess = input("\nguess a character:") 
    guesses += guess                    
    if guess not in word:  
        turns -= 1        
        print("\nWrong")    
        print("\nYou have", + turns, 'more guesses') 
        if turns == 0:           
            print ("\nYou Lose") 
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4. alarm clock

Purpose ： Write a program to create an alarm clock Python Script .

Tips ： You can use date-time Module to create alarm clock , as well as playsound The library plays sound .

from datetime import datetime   
from playsound import playsound
alarm_time = input("Enter the time of alarm to be set:HH:MM:SS\n")
alarm_hour=alarm_time[0:2]
alarm_minute=alarm_time[3:5]
alarm_seconds=alarm_time[6:8]
alarm_period = alarm_time[9:11].upper()
print("Setting up alarm..")
while True:
    now = datetime.now()
    current_hour = now.strftime("%I")
    current_minute = now.strftime("%M")
    current_seconds = now.strftime("%S")
    current_period = now.strftime("%p")
    if(alarm_period==current_period):
        if(alarm_hour==current_hour):
            if(alarm_minute==current_minute):
                if(alarm_seconds==current_seconds):
                    print("Wake Up!")
                    playsound('audio.mp3') ## download the alarm sound from link
                    break
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5. Guess the number

Purpose ： Write a guess size Python Little games .

Tips ： You can use random Randomly generate numbers .

#  Guessing game man-machine battle 
import random
target=random.randint(1,100)
count=0
while True:
      guess=eval(input(' Please enter a guess integer （1 to 100）'))
      count+=1
      if guess>target:
            print(' Guess the ')
      elif guess<target:
            print(' Guess a little ')
      else:
            print(' Guessed it ')
            break
print(' The number of guesses in this round is :',count)
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6. Mathematical addition and subtraction

Purpose ： Write a mathematical calculation Python Little games .

Tips ： You can use random Randomly generated numbers add and subtract from each other , If you answer correctly, you can enter the next level .

from random import randint
level=0                    #0 Class start 
while level<10:            # When the level is less than 10 Class time 
    a=randint(0,100)       # Randomly generate two digit integers 
    b=randint(0,100)
    c=input(f"{a}+{b}=")
    c=int(c)
    if c==a+b:             # The calculation result is correct 
        level+=1           # Level plus 1
        print(f" That's right ！ Now the level is {level} level , achieve 10 Class won ！")
    else:                  # The calculation result is wrong 
        level-=1
        print(f" Wrong answer ！ Now the level is {level}, achieve 10 Class won ！ Make persistent efforts ！")
print(f" Successfully achieve 10 level ！ Challenge success ！ awesome ！")
# Subtraction breakthrough games , Modify the above program , It should be noted that the two numbers should be compared before subtraction , Avoid negative numbers .
from random import randint
level=0                    #0 Class start 
while level<10:            # When the level is less than 10 Class time 
    a=randint(0,100)       # Randomly generate two digit integers 
    b=randint(0,100)
    if a>=b:
        c=input(f"{a}-{b}=")
        c=int(c)
        if c==a+b:             # The calculation result is correct 
            level+=1           # Level plus 1
            print(f" That's right ！ Now the level is {level} level , achieve 10 Class won ！")
        else:                  # The calculation result is wrong 
            level-=1
            print(f" Wrong answer ！ Now the level is {level}, achieve 10 Class won ！ Make persistent efforts ！")
print(f" Successfully achieve 10 level ！ Challenge success ！ awesome ！")
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​7. Guess words

Purpose ： Write an English word to fill in Python Little games .

Tips ： You can use random Randomly generate an English word , If the answer is correct ！

import random


#  A list of words ( You can fill in the words you need to recite )
words = ["print", "int", "str", "len", "input", "format", "if","for","def"]

# Initialization information ↓↓↓↓↓↓↓
def init():
    #  Declare three global variables 
    global word
    global tips
    global ranList

    # Randomly pick up a word in the word list 
    word = list(words[random.randint(0, len(words) - 1)])

    # List of random numbers , It holds random numbers that match the length of words （ No repetition ）
    ranList = random.sample(range(0, len(word)), len(word))

    # Store prompt information 
    tips = list()
    # Initialization prompt message 
    # Store underscores that match the length of words 
    for i in range(len(word)):
        tips.append("_")
    # Two letters at random 
    tips[ranList[0]] = word[ranList[0]]
    tips[ranList[1]] = word[ranList[1]]

# Function part ↓↓↓↓↓

# Display a menu 
def showMenu():
    print(" Please enter '?'")
    print(" To end the game, please enter 'quit!'")


# Display prompt message 
def showtips():
    for i in tips:
        print(i, end=" ")
    print()


# Need tips 
def needTips(tipsSize):
    # There are at least two unknown letters 
    if tipsSize <= len(word)-3:
        tips[ranList[tipsSize]] = word[ranList[tipsSize]]
        tipsSize += 1
        return tipsSize
    else:
        print(" There is no hint ！")


# Main running function ↓↓↓↓↓↓
def run():
    print("------python Keyword version -------")
    init()
    tipsSize = 2
    showMenu()
    
    while True:
        print(" Tips ：",end="")
        showtips()
        guessWord = input(" Guess the word ：")
        # ''.join(word)> hold word The contents of the list are converted to strings 
        if guessWord == ''.join(word):
            print(" congratulations , Guessed it ！ Namely %s!"%(''.join(word)))
            print(" Guess again ")
            init()
            
        elif guessWord == '?':
            tipsSize = needTips(tipsSize)
        elif guessWord == 'quit!':
            break
        else:
            print(" Wrong guess. ！")
            continue
run()
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8. Face detection

Purpose ： Write a Python Script , You can detect faces in images , And save all the faces in one folder .

Tips ： have access to haar Cascade classifiers detect faces . It returns face coordinate information , It can be saved in a file .

import cv2
# Load the cascade
face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
# Read the input image
img = cv2.imread('images/img0.jpg')
# Convert into grayscale
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
# Detect faces
faces = face_cascade.detectMultiScale(gray, 1.3, 4)
# Draw rectangle around the faces
for (x, y, w, h) in faces:
    cv2.rectangle(img, (x, y), (x+w, y+h), (255, 0, 0), 2)
    crop_face = img[y:y + h, x:x + w]  
    cv2.imwrite(str(w) + str(h) + '_faces.jpg', crop_face)
# Display the output
cv2.imshow('img', img)
cv2.imshow("imgcropped",crop_face)
cv2.waitKey()
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9. Keyboard recorder

​ Purpose ： Write a Python Script , Save all the keys pressed by the user in a text file .

Tips ：pynput yes Python One of the Libraries , It is used to control the movement of keyboard and mouse , It can also be used to make keyboard recorders . Simply read the user press

The key , And save them in a text file after a certain number of keys .

from pynput.keyboard import Key, Controller,Listener
import time
keyboard = Controller()


keys=[]
def on_press(key):
    global keys
    #keys.append(str(key).replace("'",""))
    string = str(key).replace("'","")
    keys.append(string)
    main_string = "".join(keys)
    print(main_string)
    if len(main_string)>15:
      with open('keys.txt', 'a') as f:
          f.write(main_string)   
          keys= []     
def on_release(key):
    if key == Key.esc:
        return False

with listener(on_press=on_press,on_release=on_release) as listener:
    listener.join()
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10. Short URL generator

​

Purpose ： Write a Python Script , Use API Shorten a given URL.

from __future__ import with_statement
import contextlib
try:
    from urllib.parse import urlencode
except ImportError:
    from urllib import urlencode
try:
    from urllib.request import urlopen
except ImportError:
    from urllib2 import urlopen
import sys

def make_tiny(url):
    request_url = ('http://tinyurl.com/api-create.php?' + 
    urlencode({'url':url}))
    with contextlib.closing(urlopen(request_url)) as response:
        return response.read().decode('utf-8')

def main():
    for tinyurl in map(make_tiny, sys.argv[1:]):
        print(tinyurl)

if __name__ == '__main__':
    main()
-----------------------------OUTPUT------------------------
python url_shortener.py https://www.wikipedia.org/
https://tinyurl.com/buf3qt3
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summary

All right. ！ That's what I want to share with you today , If necessary, you can collect it and look at it slowly ~

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