Python-如何在不删除内容的情况下写入文本文件

Question

我是编程新手，不知道有没有人能帮我。我已经在下面创建了一个程序，使我能够写入文本文件。我还有第三个专栏，叫做flower_quantity。我想知道如何在不覆盖flower_quantity的情况下用下面的代码更新文本文件。

def feature_4(flower_file='flowers.txt'):

    flower_update = input("Enter the name of the flower you wish to change the price:"
                          "Lily, Rose, Tulip, Iris, Daisy, Orchid, Dahlia, Peony")
    flower_new_price = input("Enter the updated price of the flower")

    flower, price = [], []
    with open(flower_file) as amend_price:

        for line in amend_price:
            spt = line.strip().split(",")
            flower_price = int(spt[1])
            flower_name = str(spt[0])

            if flower_name == flower_update :
                price.append(flower_new_price)

            else:
                price.append(flower_price)

            flower.append(flower_name)

    with open(flower_file, "w") as f_:
        for i, v in enumerate(flower):
            f_.write("{},{}\n".format(v, str(price[i])))

    print("The new price of", flower_update, "is", flower_new_price)

Answer 1

with open(path, 'a')会在附加模式下打开你的文件，它不会删除文件的内容，也不会把插入符号放在文件的末尾，所以所有的内容都会添加到文件的末尾。

您可以找到许多关于所有可用的文件打开模式的评论，例如https://stackabuse.com/file-handling-in-python/

Answer 2

在追加模式下打开文件

with open(flower_file,"a+"):

如果文件尚不存在，则+符号会创建一个新文件

这将从上次写入的点追加文件。要从新行追加，应以\n

Answer 3

有几种方法可以完成这个任务。

但是按照您已经这样做的方法，您可以在读取文件时只包含数量。代码看起来有点像这样。

def feature_4(flower_file='flowers.txt'):

    flower_update = input("Enter the name of the flower you wish to change the price:"
                          "Lily, Rose, Tulip, Iris, Daisy, Orchid, Dahlia, Peony")
    flower_new_price = input("Enter the updated price of the flower")

    flower, price, quantity = [], [], []
    with open(flower_file) as amend_price:

        for line in amend_price:
            spt = line.strip().split(",")
            flower_price = int(spt[1])
            flower_name = str(spt[0])
            quantity.append(str(spt[2]))

            if flower_name == flower_update :
                price.append(flower_new_price)

            else:
                price.append(flower_price)

            flower.append(flower_name)

    with open(flower_file, "w") as f_:
        for i, v in enumerate(flower):
            f_.write("{},{},{}\n".format(v, str(price[i]),quantity[i]))

    print("The new price of", flower_update, "is", flower_new_price)

或者，如果您确实希望更新而不覆盖整个文件，则需要使用open('txtfile.txt','a+')打开该文件。并导航到要追加的指定行。