Python 如果用户写错了，请要求用户写正确的文件名

我想使用下面的上传功能上传一些文件

我要求用户写下他想要上传的文件名

但我之前尝试过一些验证，如果用户写入的文件名不存在，我想显示一条消息您选择的文件不存在，请重试，我想再次要求用户写入相同的文件名，以便他能够正确写入。你知道我怎样才能做到这一点吗

def upload(filename):
    if(os.path.exists(filename)):
        # here I do the upload
    else:
        print "The file you selected does not exist, please try again"
        # here I want to ask user again for the field that he filled wrong
        # but this needs to be dynamic (first, second or third)
        uploadToS3(input("Select the first/second/third file:"))
print

raw_input("Press enter to transfer the files...")

upload(input("Select the first file:"))
upload(input("Select second file:"))
upload(input("Select third file:"))

由于您一步一个文件地上传文件，因此可以通过将它们锁定在循环中，在函数中一次验证一个文件。成功上载后返回循环外并运行：

def upload(filename):
    while True:
        if(os.path.exists(filename)):
            # here I do the upload
            return
        else:
            print "The file you selected does not exist, please try again"
            filename = input("Select the first/second/third file:")

---

像这样的怎么样？这是一个快速的黑客，但可能会奏效

def upload(filename):
    if(os.path.exists(filename)):
        # here I do the upload
        return True
    else:
        print "The file you selected does not exist, please try again"
        # here I want to ask user again for the field that he filled wrong
        # but this needs to be dynamic (first, second or third)
        uploadToS3(input("Select the first/second/third file:"))
print
return False

def read_user_input(prompt):
    oper_status = upload(input(prompt))
    while oper_status is not True:
        oper_status = upload(input(prompt))


raw_input("Press enter to transfer the files...")

read_user_input(input("Select the fist file:"))
read_user_input(input("Select second file:"))
read_user_input((input("Select third file:"))

---

我可能会这样做：

def get_filename(prompt):
    while True:
        fn = raw_input(prompt)
        if os.path.exists(fn): return fn
        print("The file you selected does not exist, please try again")


uploadToS3(get_filename("Select the fist file:"))
uploadToS3(get_filename("Select second file:"))
uploadToS3(get_filename("Select third file:"))

这也摆脱了你的上传功能

这种方法定义了一个名为get_filename的函数，该函数接受要显示的提示作为参数

将显示提示并收集输入

如果输入文件名存在，则返回uploadToS3

---

如果输入文件名不存在，则会打印一条消息，并提示重新发出、重新收集输入等。

尝试一个简单的while循环。当输入的文件名不存在时，while循环将保持为True。一旦用户输入一个存在的文件名，它将中断while循环并继续上传部分。当然，您应该调整编程逻辑以满足您的需要

def upload(filename):
    while True:
        if not(os.path.exists(filename)):
            print "The file you selected does not exist, please try again"
        else:
            #upload stuff
            break

---

我使用递归的答案是：

def upload(prompt):
    filename = input(prompt) #ask for filename using the given prompt
    if(os.path.exists(filename)):
        uploadToS3(filename)
    else:
        print "The file you selected does not exist, please try again"
        upload(prompt) #Repeat this function if the use did not give valid input
print

raw_input("Press enter to transfer the files...")

upload("Select the fist file:")
upload("Select second file:")
upload("Select third file:")

---

第二个输入将显示与第一个输入完全相同的消息。

这是什么意思，但需要是动态的第一、第二或第三个输入？你能详细说明一下吗？你的意思是，如果第一个输入要求第二个文件，那么函数生成的第二个输入应该要求第二个文件，依此类推？你的代码将不起作用，因为你使用的是原始输入和输入。一般来说，如果答案中包含对代码用途的解释，那么答案会更有帮助，为什么不引入其他人就解决了问题。