ファイル名がshelveモジュールが開くことができるdbでないのはなぜですか？

Question

import random 
import sys 
import shelve 

def get_input_or_quit(prompt, quit="Q"): 
    prompt += " (Press '{}' to exit) : ".format(quit) 
    val = input(prompt).strip() 
    if val.upper() == quit: 
     sys.exit("Goodbye") 
    return val 

def prompt_bool(prompt): 
    while True: 
     val = get_input_or_quit(prompt).lower() 
     if val == 'yes': 
      return True 
     elif val == 'no': 
      return False 
     else: 
     print ("Invalid input '{}', please try again".format(val)) 


def prompt_int_small(prompt='', choices=(1,2)): 
    while True: 
     val = get_input_or_quit(prompt) 
     try: 
      val = int(val) 
      if choices and val not in choices: 
       raise ValueError("{} is not in {}".format(val, choices)) 
      return val 
     except (TypeError, ValueError) as e: 
       print(
        "Not a valid number ({}), please try again".format(e) 
        ) 

def prompt_int_big(prompt='', choices=(1,2,3)): 
    while True: 
     val = get_input_or_quit(prompt) 
     try: 
      val = int(val) 
      if choices and val not in choices: 
       raise ValueError("{} is not in {}".format(val, choices)) 
      return val 
     except (TypeError, ValueError) as e: 
       print(
        "Not a valid number ({}), please try again".format(e) 
        ) 

role = prompt_int_small("Are you a teacher or student? Press 1 if you are a student or 2 if you are a teacher") 
if role == 1: 
    score=0 
    name=input("What is your name?") 
    print ("Alright",name,"welcome to your maths quiz." 
      " Remember to round all answers to 5 decimal places.") 
    level_of_difficulty = prompt_int_big("What level of difficulty are you working at?\n" 
           "Press 1 for low, 2 for intermediate " 
            "or 3 for high\n") 


    if level_of_difficulty == 3: 
     ops = ['+', '-', '*', '/'] 
    else: 
     ops = ['+', '-', '*'] 

    for question_num in range(1, 11): 
     if level_of_difficulty == 1: 
      max_number = 10 
     else: 
      max_number = 20 

     number_1 = random.randrange(1, max_number) 
     number_2 = random.randrange(1, max_number) 
     operation = random.choice(ops) 

     maths = round(eval(str(number_1) + operation + str(number_2)),5) 
     print('\nQuestion number: {}'.format(question_num)) 
     print ("The question is",number_1,operation,number_2) 
     answer = float(input("What is your answer: ")) 
     if answer == maths: 
      print("Correct") 
      score = score + 1 
     else: 
      print ("Incorrect. The actual answer is",maths) 

    if score >5: 
     print("Well done you scored",score,"out of 10") 
    else: 
     print("Unfortunately you only scored",score,"out of 10. Better luck next time") 


    class_number = prompt_int_big("Before your score is saved ,are you in class 1, 2 or 3? Press the matching number") 

    filename = (str(class_number) + "txt") 
    with shelve.open(filename) as db: # This is the effected line 
     old_scores = db.get(name, []) 
     old_scores.extend(score) 
     db[name] =score[-3:] 


    if prompt_bool("Do you wish to view previous results for your class"): 
     for line in lines: 
      print (line) 
    else: 
     sys.exit("Thanks for taking part in the quiz, your teacher should discuss your score with you later") 

if role == 2: 
    class_number = prompt_int_big("Which class' scores would you like to see? Press 1 for class 1, 2 for class 2 or 3 for class 3") 
    filename = (str(class_number) + "txt") 
    sort_or_not = int(input("Would youlike to sort these scores in any way? Press 1 if the answer is no or 2 if the answer is yes")) 
    if sort_or_not == 1: 
     f = open(filename, "r") 
     lines = [line for line in f if line.strip()] 
     lines.sort() 
     for line in lines: 
      print (line) 
    if sort_or_not == 2: 
     type_of_sort = int(input("How would you like to sort these scores? Press 1 for scores in alphabetical order with each student's highest score for the tests, 2 if you would like to see the students' highest scores sorted from highest to lowest and 3 if you like to see these student's average scores sorted from highest to lowest")) 
     if type_of_sort == 1: 
      with open(filename , 'r') as r: 
       for line in sorted(r): 
        print(line, end='') 
     if type_of_sort == 2: 
      file = open(filename, 'r') 
      lines = file.read().splitlines() 
      s = {lines[i]:[int(k) for k in lines[i+1:i+4]] for i in range(0,len(lines),4)} 
      for i in sorted(s.keys()): 
       print (i,max(s[i])) 

      avg_mark = lambda name:sum(s[name])/len(s[name]) 
      for i in sorted(s.keys(),key=avg_mark,reverse=True): 
       print (i,avg_mark(i)) 
     if type_of_sort == 3: 
      file = open(filename, 'r') 
      lines = file.read().splitlines() 
      s = {lines[i]:[int(k) for k in lines[i+1:i+4]] for i in range(0,len(lines),4)} 
      for i in sorted(s.keys()): 
       print (i,max(s[i])) 

      high_mark = lambda name:max(s[name]) 
      for i in sorted(s.keys(),key=high_mark,reverse=True): 
       print (i,high_mark(i)) 

私のコードのshelveモジュールの部分が動作していないため、エラーの内容を理解できません。最後の3つの得点を生徒の名前に保存して、さまざまな方法で並べ替えることを試みています。クイズが学生として完了した後、エラーが表示されます。

Answer 1

filenameでファイルを削除し、スクリプトを再度実行して、データベースファイルを正しい形式で作成するようにしてください。空のファイルや他の手段（CSV、JSONなど）で作成されたファイルを開くように依頼した場合、そのファイルを処理する方法はわかりません。