拋出異常

Question

後，我感到有一些問題，我的家庭作業的結構蟒蛇&初學者如何讓我的Python代碼走回到環路;我的任務是：「編寫一個程序，要求用戶輸入文件名，打開文件並讀取文件一次，然後向用戶報告字符數（包括空格和行尾字符），字數，以及文件中的行數

如果用戶輸入了一個不存在的文件的名稱，那麼程序應該給她儘可能多的嘗試，以便輸入一個有效的文件名。來自用戶的有效文件名是一種常用操作，因此首先編寫一個單獨的可重複使用的函數，該函數會重複詢問用戶的文件名，直到她鍵入文件中的程序能夠打開。 而且，我也沒有啓動方式（&現在我想知道如果用我的方式已經與它的結構「與/爲」，有一個辦法，甚至這樣做，但現在我的問題越來越它去在拋出錯誤後回到代碼的try部分（我錯過了解釋這個的類，所以我只讀過這個，所以我知道我沒有做正確的事情）。我可以讓它工作很長時間因爲它的存在，如果它不是一個文件名，不打印輸出到屏幕下面是我的代碼：

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，我不知道我該怎麼做 - 我是否應該放棄了這個整體思路簡單的嘗試：開放（文件名，「R」）/除外：它的功能= F有反正挽救這個

所以，我認爲解決這個問題是這樣的：

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，我發現了錯誤：NameError: name 'file' is not defined

Answer 1

寫一個無限循環while True。當文件名正確時，在try的末尾添加break。

高興的是，幫助

Answer 2

，以使文件在循環中打開我會整理這些代碼。無論用戶輸入多少次無效的文件名，代碼都會要求一個新的文件名並重試。

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)