使用函數時發生Python代碼錯誤

Question

我有此代碼，我希望它根據需要多次詢問該問題，直到給出是或否的答案為止

def teacheraskno():
teacher = input("Are you a teacher? yes and no answers only! > ")
if teacher == "no" or "yes".lower():
    if teacher == "no".lower():
        start()
    if teacher == "yes".lower():
        teacheraskyes()
else:
    print ("Please enter yes and no answers only!")
    teacheraskno()

def teacheraskyes():
if teacher == "yes".lower(): 
    password = input("What is the Password? > ")
if password =="123".lower(): 
    print ("ACCESS GRANTED!")
    classname = input("what class would you like to view? 1, 2 or 3 > ")

    f = open(classname + ".txt", 'r') #opens the class file
    file_contents = f.read()
    print (file_contents)
    f.close()


teacher = input("Are you a teacher? yes and no answers only! > ")
if teacher == "no" or "yes".lower():
    if teacher == "no".lower():
        start()
    if teacher == "yes".lower():
        teacheraskyes()
    else:
        print ("Please enter yes and no answers only!")
        teacheraskno()

我不斷收到這個錯誤

==============================Math Revision Quiz================================
Are you a teacher? yes and no answers only! > bla
Please enter yes and no answers only!
Are you a teacher? yes and no answers only! > yes
Traceback (most recent call last):
  File "S:\My Documents\Ben Atia CA A453\Python Code\Python Code 1.py", line 142, in <module>
    teacheraskno()
  File "S:\My Documents\Ben Atia CA A453\Python Code\Python Code 1.py", line 118, in teacheraskno
    teacheraskyes()
  File "S:\My Documents\Ben Atia CA A453\Python Code\Python Code 1.py", line 125, in teacheraskyes
    if password =="123".lower(): #if the password is correct it will let the teacher view the code
UnboundLocalError: local variable 'password' referenced before assignment
>>> 

此錯誤是什么意思，我該如何解決？
請幫我解決這個問題。

Answer 1

您應該更改此行

if teacher == "no" or "yes".lower():

至

if teacher.lower() not in ("no", "yes"):

就目前而言，該表達式並不表示您認為的含義。 如果我加括號以強調，您的表達實際上為

if (teacher == "no") or ("yes".lower()):

子表達式"yes".lower()將始終產生True 。

Answer 2

鑒於您的摘要的縮進，很難確定，但是在這里：

if teacher == "yes".lower(): 
    password = input("What is the Password? > ")
if password =="123".lower(): 
    print ("ACCESS GRANTED!")

您只能在第一個if分支中定義password變量，但是在兩種情況下都嘗試讀取它。 因此，如果teacher不等於“是”，則未定義password 。

您的代碼還有很多其他問題，但這超出了您的問題范圍。

Answer 3

代替.lower您可以在input()之前使用str.casefold() input() 。 這會使用戶輸入的任何內容都變成小寫。 這不僅是一種驗證，而且還允許您以小寫形式編寫所有代碼。 例如：

teacher = str.casefold(input("Are you a teacher?"))

這應該更改用戶輸入的所有小寫字母，而沒有.lower()函數的情況下，代碼的結果可以用小寫字母編寫。