Python：您如何基于前一行从文本文件中读取特定行？

Question

I apologize if this is a duplicate, but I couldn't find anything that matched my specific question. I am creating a project that acts like a bank system and reads username, password, and amount from a text file. I have a text file set up with username on first line, password on second line, and amount on third and then another block that has same pattern. I am checking if the username that the user inputs is in the file, then checks the next line and checks if the password enters is the next line.

f = open_file("D:/PythonProjects/banking.txt", "r") #open file   
read_file = f.read() #store contents of file in variable
name = input("Username: ")
pword = input("Password: ")
if name in read_file: #check if username is in file contents variable
    if pword in read_file:
       print("match")

So far, this prints 'match' if you enter name/password in the file, but I'm only looking for the matching password. I also have a function that returns the next line and tried to call that twice in order to get the line after the name line.

def next_line(the_file):
'''Returns the next line from the_file'''
line = the_file.readline()
line = line.rstrip()
return line

Answer 1

Security (encryption) and efficiency (database) issues mentioned in the other answers aside, here is a possible solution parsing your file directly into a dictionary:

data = {}
filename = "D:/PythonProjects/banking.txt"
with open(filename, "r") as fh:
    username = ""
    password = ""
    amount = -1

    line_mode = 1
    for line in fh:
        if line_mode % 3 == 1:
            username = line.strip()
            data[username] = {}
        elif line_mode % 3 == 2:
            password = line.strip()
            data[username][password] = -1
        elif line_mode % 3 == 0:
            amount = float(line.strip())
            data[username][password] = amount

        line_mode += 1 

input_name = input("Username: ")
input_password = input("Password: ")

if input_name in data and input_password in data[input_name]:
    print("amount", data[input_name][input_password])
else:
    print("User not found or password incorrect")

EDIT: A shorter solution came into my mind:

filename = "D:/PythonProjects/banking.tx"
data = {}

with open(filename, "r") as fh:
    lines = [line.strip() for line in fh.readlines()]
    for i in range(0, len(lines), 3):
        data.setdefault(lines[i], {})[lines[i+1]] = lines[i+2]

lines[i] , lines[i+1] , lines[i+3] are the username, password and amount.

dict.setdefault(key, default) either returns the value in data for the key lines[i] , ie the entry for a username, if it is already present, or creates a new dict with the username as key and returns it afterwards. It is now ensured that data[lines[i]] exists and can be filled with the password ( lines[i+1] ) and amount ( lines[i+2] ).

Answer 2

Better use a database. SQLite is good starting point. You don't even have to install anything (since SQLite is already included with Python). Have fun.