Python/列表/文件/循環/追加

Question

我必須打開一個文件並循環遍歷列表。 然后我必須打印結果並將某些行附加/寫入同一文件。 我希望能夠多次運行代碼，但我不想 append 某些行多次，我也不想閱讀附加的行。 問題是 - 如何僅附加/寫入一次以及如何跳過讀取附加行？ 這是代碼：

kitty = 500

requests = []

file = open("loan_requests.txt", "r+")

requests = file.readlines()


for item in requests:

    flag = bool(int(item))
    if flag == False:
        break

    
    if  int(item) <= kitty and kitty > 0:
            kitty = kitty - int(item)
            loan = int(item)
            print(loan, "- Paid!")
            file.write("Request of {} paid in full.\n".format(loan))
        
    elif int(item) > kitty and kitty > 0:
             kitty = kitty - int(item)
             loan = int(item) + kitty
             print(int(item), "Request cannot be processed in full (Insufficient funds available). Amount paid:", loan)
             file.write("Request of {} could not be paid in full.Partial payment of {} made.\n".format(item, loan))

    elif int(item) > kitty and kitty <= 0:
             print("Request of", int(item), "is UNPAID!")
             file.write("Outstanding Request:{}\n".format(item))


file.close()



Tried with seek(); tell(). 

Answer 1

在寫入文件之前，檢查文件是否已經包含該行。

kitty = 500

requests = []

file = open("loan_requests.txt", "r+")

requests = file.readlines()

def write_new(file, line, requests):
    if line not in requests:
        file.write(line)

for item in requests:
    
    if int(item) < kitty and kitty > 0:
        kitty = kitty - int(item)
        loan = int(item)
        write_new(file, "Request of {} paid in full.\n".format(loan), requests)
        print(loan, "- Paid!")

    elif int(item) > kitty and kitty > 0:
        kitty = kitty - int(item)
        loan = int(item) + kitty
        write_new(file, "Request of {} could not be paid in full.Partial payment of {} made.\n".format(item, loan), requests)
        print(int(item), "request cannot be processed in full (Insufficient funds available). Amount paid:", loan)
            
    elif int(item) > kitty and kitty <= 0:
        write_new(file, "Outstanding Request:{}\n".format(item), requests)
        print("Request of", int(item), "is UNPAID!")

file.close()

Answer 2

轉換 Barman 的建議，讓我們從 helper function 開始，它是否會寫入取決於一些標志：

SHOULD_WRITE = True
def maybe_write(file, message):
    if SHOULD_WRITE:
        file.write(message)

現在使用 function 而不是file.write ：

# file.write("Request of {} paid in full.".format(loan))
maybe_write(file, f"Request of {loan} paid in full.")

下次，更改SHOULD_WRITE = False的值

獎勵：你知道python有這么花哨的語法嗎？

if 0 < kitty < int(item):
    ...

Answer 3

kitty = 500
requests = []
file = open('loan_requests.txt')

for line in file:
    if line.strip().isdecimal():
        requests.append(int(line))

file.close()


with open('loan_requests.txt', 'a') as file:

    for request in requests:

        if request <= kitty:
            file.write('\nRequest of ' + str(request) + ' paid in full.')
            print(str(request) + ' - Paid!')
            kitty -= request