如何使用 python 处理将值添加到具有现有值的 txt 文件的第一行

Question

如需文件处理方面的帮助，请：

所以，我是 Python 的新手，我决定直接写一个小程序。基本上，想法是有一个 .txt 文件，在一行中保持运行平衡，这是从用户输入接收的。但是，我很难理解如何将用户输入写入单行的值。话虽如此，这就是我必须提供的参考：

print("\n"""" Please choose an option: 
    Balance:
        1. View
        2. Update
    -------------    
    Savings: 
        3. View
        4. Update""""\n") 
number = int(input(" Enter a number: ")) 
if number == 1:
    view = open("current_balance.txt", "r")
    print("\n", "Balance: " + view.read())
elif number == 2: 
    new_entry = input("\n" + " Enter figure: ")  
    update_balance = open("current_balance.txt", "a+")          
    update_balance.write(new_entry)
    update_balance = open("current_balance.txt", "r")
    print(update_balance.read())
    update_balance.close()
elif number == 3:
    print("test")
elif number == 4: 
    print("test")

如果问的不是太多，一些一般性的指导会很好。谢谢！

Answer 1

如果我对你的问题的理解正确，你想在新的一行上写下新的余额，同时跟踪旧的余额。您可以做的是以下

print("\n"""" Please choose an option: 
    Balance:
        1. View
        2. Update
    -------------    
    Savings: 
        3. View
        4. Update""""\n")
number = int(input(" Enter a number: "))
if number == 1:
    view = open("current_balance.txt", "r")
    print("\n", "Balance: " + view.read())
elif number == 2:
    new_entry = input("\n" + " Enter figure: ")
    update_balance = open("current_balance.txt", "a")
    update_balance.write(new_entry + "\n")
    update_balance = open("current_balance.txt", "r")
    balances= list(map(int, update_balance.readlines()))
    total_balance = sum(balances)
    print(balances, "\n", total_balance)
    update_balance.close()
elif number == 3:
    print("test")
elif number == 4:
    print("test")

Answer 2

据我了解

View：应显示余额（存储为文件的第一行）
Update：应将用户输入值与现有余额值相加，并将这两者的总和写在第一行。

这是您需要的代码。

print("\n"""" Please choose an option: 
    Balance:
        1. View
        2. Update
    -------------    
    Savings: 
        3. View
        4. Update""""\n") 
number = int(input(" Enter a number: ")) 
if number == 1:
    view = open("current_balance.txt", "r")
    print("\n", "Balance: " + view.read())
    view.close()
elif number == 2: 
    new_entry = input("\n" + " Enter figure: ") 
    update_balance = open("current_balance.txt", "r")
    
    # The first line of the file - Existing Balance
    existing_val = update_balance.read()
    
    update_balance = open("current_balance.txt", "w")
    # If the first line is not empty, Add User's input value and existing value and write the sum to the file.
    if existing_val != "":
        value = int(new_entry) + int(existing_val)
        update_balance.write(str(value) + '\n')
    else:
        update_balance.write(new_entry)
    
    update_balance = open("current_balance.txt", "r")
    print(update_balance.read())
    update_balance.close()
elif number == 3:
    print("test")
elif number == 4: 
    print("test")

如何使用 python 处理将值添加到具有现有值的 txt 文件的第一行

How to handle adding a value to first line of txt file that has an existing value using python

python

if-statement

file

input

file-handling