Python程序：讀取文件

Question

我應該編寫一個程序，它不斷地向用戶提供一個文件名，直到它輸入正確的文件名爲止。然後，find_min_percent應該接受一個參數，GDP.txt文件中的一行（str）然後遍歷該行以找到最小值並返回該值。這裏是我的代碼到目前爲止

line = " " 

def open_file(): 
    ''' Repeatedly prompt until a valid file name allows the file to be opened.''' 
    while True: 
     user_input = input('Enter a file name: ') 
     try: 
      file = open(user_input, 'r') 
      return file 
      break 
     except FileNotFoundError: 
      print('Error. Please try again') 
      open_file() 

def find_min_percent(line): 
    '''Find the min percent change in the line; return the value and the index.''' 
    percent_lst = [] 
    line = file.readline(9) 
    percent_lst += [line] 
    percent_int = [float(i) for i in percent_lst] 
    min_value = 10000 
    for percent in percent_int: 
     if percent < min_value: 
      min_value = percent 
      return min_value 


print(open_file()) 
print (find_min_percent(line)) 

我的問題是與readline（）。它說變量文件是未定義的。此代碼的大綱不包含「def find_min_percent（line）：」部分中的文件。所以我不知道如何去解決這個問題。我也不能在函數之外設置行，因爲我必須在程序的其他函數中使用相同的行變量來讀取其他行。所以我不知道該怎麼做才能保持不變

Answer 1

您在一個函數中定義的變量不能從另一個函數訪問。爲了解決這個問題，你可以舉例來說，做到這一點（存儲在一個「主要功能」變量返回的值，並把它傳遞給你的下一個函數）：

def find_min_percent(line): 
    '''Find the min percent change in the line; return the value and the index.''' 
    percent_lst = [] 
    # You can use f from this function, as long as you don't modify it 
    line = f.readline(9) 
    percent_lst += [line] 
    percent_int = [float(i) for i in percent_lst] 
    min_value = 10000 
    for percent in percent_int: 
     if percent < min_value: 
      min_value = percent 
      return min_value 


f = open_file() 
print(f) 
print (find_min_percent(line)) 

順便說一句，你用你的line變量的方式很奇怪。它僅在find_min_percent內部使用，但在函數的外部定義，甚至作爲參數傳遞。爲什麼？你想達到什麼目的？

（參見here用於關於功能之外定義變量的訪問郵政）

Answer 2

返回file變量超出該函數的範圍 固定編碼的：

line = " " 

def open_file(): 
    ''' Repeatedly prompt until a valid file name allows the file to be opened.''' 
    while True: 
     user_input = input('Enter a file name: ') 
     try: 
      file = open(user_input, 'r') 
      return file 
      break 
     except FileNotFoundError: 
      print('Error. Please try again') 
      open_file() 

def find_min_percent(line,file): 
    '''Find the min percent change in the line; return the value and the index.''' 
    percent_lst = [] 
    line = file.readline(9) 
    percent_lst += [line] 
    percent_int = [float(i) for i in percent_lst] 
    min_value = 10000 
    for percent in percent_int: 
     if percent < min_value: 
      min_value = percent 
      return min_value 

temp=open_file() 
print(temp) 
print (find_min_percent(line,temp)) 

Answer 3

的另一種方式這樣做：

def open_file(): 
    ''' Repeatedly prompt until a valid file name allows the file to be opened.''' 
    while True: 
     user_input = input('Enter a file name: ') 
     try: 
      file = open(user_input, 'r') 
      print('user_input: ', user_input) 
      line = file.readline(9) 
      file.close() 
      return find_min_percent(line) 
     except FileNotFoundError: 
      print('Error. Please try again') 
      open_file() 

def find_min_percent(line): 
    '''Find the min percent change in the line; return the value and the index.''' 
    percent_lst = [] 
# line = file.readline(9) 
    percent_lst += [line] 
    percent_int = [float(i) for i in percent_lst] 
    min_value = 10000 
    for percent in percent_int: 
     if percent < min_value: 
      min_value = percent 
      return min_value 


print(open_file()) 

請注意，我不是sur e關於您的find_min_percent方法的正確性。另外，如果您手動打開文件（不使用with open），則還需要明確關閉。