此问题在此处已有答案：

Asking the user for input until they give a valid response（22个答案）
昨天关闭。

print("ax^2 + bx + c = 0")

def ask_a():
    a = int(input("""Please enter a:
a = """))
    if a == 0:  
        print("Please input the correct number! \n")
        a = int(input("""Please enter a:
a = """))
    else:
        try:
            a == int(a)
            print(f"a = {a}")
        except ValueError:
            print("Please input the correct number! \n")
            a = int(input("""Please enter a:
a = """))

a =  ask_a()

错误消息：

Traceback (most recent call last):
  File "c:\Users\jbtua\OneDrive\Desktop\wut is this\Personal Folder\Programming Projects\Python\blank.py", line 19, in <module>
    a =  ask_a()
  File "c:\Users\jbtua\OneDrive\Desktop\wut is this\Personal Folder\Programming Projects\Python\blank.py", line 4, in ask_a
    a = int(input("""Please enter a:
ValueError: invalid literal for int() with base 10: 'a'

我仍然不知道这是什么原因。