无法追加到文件

Question

我正在尝试编写这个程序，如果用户打开现有文件，他们可以选择读取、重新开始或附加到它，但附加选项不起作用。这是为什么呢？

from sys import argv

file = input("Please open a file: ")
try:
    file = open(file, "r+")
    choice = input("""
    What would you like to do with this file?
    A) Read file
    B) Delete file and start over
    C) Append file
    """).lower().rstrip()
    if choice in "a":
        print(file.read())
    elif choice in "b":
        print("What would you like to write?")
        file.write(input())
    elif choice in "c":
        file = open(file, "a")
        print("What would you like to write?\n")
        file.write(input())
except:
    print("This is a new file.\n")
    file = open(file, "w")
    print("What would you like to save in this file?")
    file.write(input())```

Answer 1

您的代码的问题是您将变量file 分配给input("Please open a file: ") 中的用户输入，但在此之后您将其分配为file = open(file, "r+") 中的txt 文件。

因此，当您编写file = open(file, "a") 时，编译器读取的file 不是作为用户输入，而是作为打开的txt 文件。

你应该做的是给不同的变量起不同的名字

from sys import argv

filename = input("Please open a file: ")
try:
    file = open(filename, "r+")
    choice = input("""
    What would you like to do with this file?
    A) Read file
    B) Delete file and start over
    C) Append file
    """).lower().rstrip()
    if choice in "aA":
        print(file.read())
    elif choice in "bB":
        print("What would you like to write?")
        file.write(input())
    elif choice in "cC":
        file.close()
        file = open(filename, "a")
        print("What would you like to write?\n")
        file.write(input())
except:
    print("This is a new file.\n")
    file = open(file, "w")
    print("What would you like to save in this file?")
    file.write(input())

更新

正如 OneLiner 在 cmets 中所说，您应该始终在打开文件后关闭它们。正如他所说，这可以通过使用with open(filename, "a") as file: 轻松完成。除此之外，我还注意到了两件事。

首先，您不应该单独使用except，因为如果我尝试按ctrl+c，它将属于此异常。你应该写except FileNotFoundError，这样如果没有这样的文件，就会引发这个异常。

我注意到的第二件事是您使用名称file 作为变量的名称。问题是 file 已经在 python 中用于另一件事，所以最好使用另一个名称。在这种情况下，代码将是：

from sys import argv

filename = input("Please open a file: ")

try:
    with open(filename, "r+") as file_txt:
        pass

    choice = input("""
    What would you like to do with this file?
    A) Read file
    B) Delete file and start over
    C) Append file
    """).lower().rstrip()

    if choice == "a":
        with open(filename, "r") as file_txt: 
            print(file_txt.read())
    elif choice == "b":
        content = input("What would you like to write?\n")
        with open(filename, "w") as file_txt:
            file_txt.write(content)
    elif choice == "c":
        with open(filename, "a") as file_txt:
            content = input("What would you like to write?\n")
            file_txt.write(content)
            
except FileNotFoundError:
    print("This is a new file.\n")
    with open(filename, "w") as file_txt:
        content = input("What would you like to save in this file?\n")
        file_txt.write(content)

Answer 2

使用"r+" 可以读写，但是指针在开头，这意味着“附加”实际上并不存在。如果我没记错的话，没有办法打开文件进行读取、写入和追加，因为没有办法沿着文件移动指针。

为了解决这个问题，我建议在每个 if 子句中单独打开文件。

如果此人想要阅读该文件，请使用"r" 打开它。 如果此人想要写入文件，则使用"w"打开它，如果此人想要追加到它，则使用"a"打开它。更多选项，例如两者的组合可以找到here。

代码：

try:
    #removed:
    #file = open(file, "r+")
    choice = input("""
    What would you like to do with this file?
    A) Read file
    B) Delete file and start over
    C) Append file
    """).lower().rstrip()
    if choice in "a":
        file = open(file, "r")
        print(file.read())
    elif choice in "b":
        file = open(file, "w")
        print("What would you like to write?")
        file.write(input())
    elif choice in "c":
        file = open(file, "a")
        print("What would you like to write?\n")
        file.write(input())
except:
    print("This is a new file.\n")
    file = open(file, "w")
    print("What would you like to save in this file?")
    file.write(input())