python beginner user login implementation process of example explains

Required to write login interface:

1. Enter your username and password

2. Welcome message will be displayed after successful authentication

3. User name input error, prompt the user does not exist, re-input (5 errors, prompt too many attempts, exit the program)

4. User name is correct, password is wrong, prompt password is wrong, re-enter (password is wrong 3 times, lock user name and prompt, exit the program)

readme

Application knowledge:

1. Operation of documents

Basic operation

f = open('lyrics','r',) # Open the file 
first_line = f.readline()
print('first line:',first_line) # read 1 line 
data = f.read()#  Read all the rest , Don't use the file when it is large 
print(data) # Print documents 
f.close() # Close the file 

The mode to open the file is as follows:

r, read-only mode (default).

w, write mode only. 【 unreadable; create if it does not exist; delete if it does exist; 】

a, append mode. [Readable; created if it does not exist; appended if it does exist;]

with statement, open multiple files at the same time, also can avoid open the file after forgetting to close, syntax:

with open('file1', 'r', encoding='utf-8') as f , \
open('file2', 'w', encoding='utf-8') as f_2 :
...

In this example, there are two files, one with username and password, and the other with blacklist. How to convert the file into python object after reading it, and then operate on the object, is the first difficulty I encountered!

And then I look it up, and I find the string split method, which breaks the string from the comma separator, and I get a list of substrings, so that I can find the blacklist and so on.

...
user_lis_bak = f.readline().split(',')
...

The setdefault dictionary setdefault() function is similar to the get() method in that if the key does not already exist in the dictionary, the key is added and the value is set to the default.

dict.setdefault(key, default=None) 

Lists and dictionaries

List is one of the most commonly used data types in the future. Through list, data can be stored and modified in the most convenient way

names = ['xiaoli',"xiaoming",'yuanlu'] 

Access elements in a list with subscripts that count from 0

>>> names[0]
'xiaoli'
>>> names[1]
'xiaoming'
>>> names[-1]
'yuanlu'
>>> names[-2] # You can also do it backwards 
'xiaoming'

A dictionary is a data type of ES57en-ES58en. Use a dictionary like the one we used in school. Use the strokes and letters to look up the details of the corresponding page.

 info = {
   'xiaoli': "123456",
   'xiaoming': "111111",
   'yuanlu': "888888",
 }

Here key is the username,value is the password,11 corresponds, and key is the only one.

3. for loop and if... else

for i in range(10): print(i) 

The above procedure, but encountered more than 5 cycles do not go, direct exit

 for i in range(10):
   if i>5:
     continue # It's not going down , Go straight down 1 time loop
   print(i)

User name and password file format:

xiaoli 123456

xiaoming 888888

wangpeng 111111

luyuan 112222

qiling 556666

haiming 223333

Blacklist file format:

xiaoli,xiaoming,wangpeng,

code

with open('user_lis', 'r', encoding='utf-8') as f_user_lis,\
     open('user_lis_bak', 'r', encoding='utf-8') as f_user_lis_bak: #  Open the file 'user_lis' and 'user_lis_bak'
  user_lis_bak = f_user_lis_bak.read().split(',')   #  read f_user_lis_bak And turn into a list to assign to  user_lis_bak
  user_lis_dict = {}                 #  define 1 An empty dictionary 
  for i in f_user_lis:
    user_lis_dict.setdefault(i.split()[0], i.split()[1])  #  read f_user_lis And put the value in the dictionary user_lis_dict In the 
count = 0
for i in range(5):                 #  Set the maximum number of errors to 5 time 
  name = input(' Please enter the user name >>')
  password = input(' Please enter your password. >>')
  if name in user_lis_bak:            #  The first 1 First, look for the blacklist 
    print(' The user name is locked , Please contact the administrator !!!')
    continue                  #  Go directly to the blacklist 1 loops , Re-enter the username and password 
  elif name in user_lis_dict:           #  The first 2 Step To find the user whitelist 
    if password == user_lis_dict.get(name):   #  Password is correct , Verification by   exit 
      print(' Dear Member ', name, ' Welcome back ')
      break
    else:                   #  Password mistake , Prompt error 
      if count == 2:
        name_bak_write = open('user_lis_bak', 'a', encoding='utf-8')
        name_bak_write.write(name+',')
        name_bak_write.close()       # 3 Secondary password error , Just put the username on the blacklist 
        print(' The user name is locked , Please contact the administrator !!!')
        break
      print(' Password mistake !!!')
      count += 1               #  The password is wrong 1 time ,count it +1
  else:
    if i == 4:                 #  The user name wrong 5 time , Directly out of 
      print(' Too many attempts , goodbye !!!')
      continue
    print(' The username does not exist !!!')          #  User name error , Prompt error