抛出异常

Question

后，我感到有一些问题，我的家庭作业的结构蟒蛇&初学者如何让我的Python代码走回到环路;我的任务是：“编写一个程序，要求用户输入文件名，打开文件并读取文件一次，然后向用户报告字符数（包括空格和行尾字符），字数，以及文件中的行数

如果用户输入了一个不存在的文件的名称，那么程序应该给她尽可能多的尝试，以便输入一个有效的文件名。来自用户的有效文件名是一种常用操作，因此首先编写一个单独的可重复使用的函数，该函数会重复询问用户的文件名，直到她键入文件中的程序能够打开。 而且，我也没有启动方式（&现在我想知道如果用我的方式已经与它的结构“与/为”，有一个办法，甚至这样做，但现在我的问题越来越它去在抛出错误后回到代码的try部分（我错过了解释这个的类，所以我只读过这个，所以我知道我没有做正确的事情）。我可以让它工作很长时间因为它的存在，如果它不是一个文件名，不打印输出到屏幕下面是我的代码：

filename = input("please enter a file name to process:") 



lineCount = 0 
wordCount = 0 
charCount = 0 
try: 

    with open(filename, 'r') as file: 
     for line in file: 
      word = line.split() 
      lineCount = lineCount + 1 
      wordCount = wordCount + len(word) 
      charCount = charCount + len(line) 

    print("the number of lines in your file is:", lineCount) 
    print("the number of words in your file is", wordCount) 
    print("the number of characters in your file is:", charCount) 

except OSError: 

    print("That file doesn't exist") 
    filename = input("please enter a file name to process:") 

而且，我不知道我该怎么做 - 我是否应该放弃了这个整体思路简单的尝试：开放（文件名，“R”）/除外：它的功能= F有反正挽救这个

所以，我认为解决这个问题是这样的：

def inputAndRead(): 
"""prompts user for input, reads file & throws exception""" 
filename = None 
    while (filename is None): 
     inputFilename = input("please enter a file name to process") 
     try: 
      filename = inputFilename 
      open(filename, 'r') 
     except OSError: 
      print("That file doesn't exist") 
    return filename 



inputAndRead() 

lineCount = 0 
wordCount = 0 
charCount = 0 

with open(filename, 'r') as file: 
for line in file: 
    word = line.split() 
    lineCount = lineCount + 1 
    wordCount = wordCount + len(word) 
    charCount = charCount + len(line) 

print("the number of lines in your file is:", lineCount) 
print("the number of words in your file is", wordCount) 
print("the number of characters in your file is:", charCount) 

但是，我发现了错误：NameError: name 'file' is not defined

Answer 1

写一个无限循环while True。当文件名正确时，在try的末尾添加break。

高兴的是，帮助

Answer 2

，以使文件在循环中打开我会整理这些代码。无论用户输入多少次无效的文件名，代码都会要求一个新的文件名并重试。

lineCount = 0 
wordCount = 0 
charCount = 0 

f = None 
while f is None: 
    filename = input("please enter a file name to process:") 
    try: 
     f = open(filename) 
    except OSError: 
     print("That file doesn't exist") 

for line in file: 
    word = line.split() 
    lineCount = lineCount + 1 
    wordCount = wordCount + len(word) 
    charCount = charCount + len(line) 

print("the number of lines in your file is:", lineCount) 
print("the number of words in your file is", wordCount) 
print("the number of characters in your file is:", charCount)