Python中ATM程序的交易记录

Question

My assignment is to keep a record of the transactions of an ATM program in a text file. After every deposit or withdraw you must update the file with the transaction type, amount deposited/withdrawn, and updated balance. I am able to get the text file to print out the current balance but only for one deposit/withdraw. Additionally, when the program runs it is supposed to open the file with the transactions and find the current balance for the account, but each time I run the program the new text just replaces the old. Here is my code:

balancefile=open("balancefile.txt", "w")
balancefile.write("Starting balance is $10000 \n")
USER_BALANCE=10000
name=input("What is your name? ")
print(name +"," + " " + "Your current balance is: $" + str(USER_BALANCE))
while True:
    answer=input("Would you like to deposit, withdraw, check balance, or exit? ")
    if answer=="deposit" or answer== "Deposit":
        x= input("How much would you like to deposit? ")
        USER_BALANCE += float(x)
        print (name + "," + " " + "Your new balance is: $" + str(USER_BALANCE))
        balancefile.write("You have deposited an amount of $" + x + "." + " " + "Current balance is $" + str(USER_BALANCE) +"\n")
        continue
    elif answer== "withdraw" or answer== "Withdraw":
        y= input("How much would you like to withdraw? ")
        if float (y)<=USER_BALANCE:
            USER_BALANCE -= float(y)
            print (name + "," + " " + "Your new balance is: $" + str(USER_BALANCE))
            balancefile.write("You withdrew an amount of $" + y + "." + " " + "Current balance is $" + str(USER_BALANCE) + "\n")
            continue
        else:
            print ("Cannot be done. You have insufficient funds.")
    elif answer== "check balance" or answer== "Check Balance":
        print ("$" + str(USER_BALANCE))
    elif answer== "exit" or answer== "Exit":
        print ("Goodbye!")
        balancefile.close()
        break
    else:
        print ("I'm sorry, that is not an option")

Please help! To clarify, the original amount in the account is $10,000 but you are supposed to be able to re-enter the program after exiting using the last updated balance in the text file.

Answer 1

As the commenters have noted , the file mode 'w' will truncate the file proir to write, and 'a' will open a file for appending. This is described in further detail in the Python documentation .