python - Python if 语句不起作用？

Question

我刚刚开始学习python，通过“像计算机科学家一样思考”这本书，我陷入了一些语言语法。

def amt():
    amount = input("Enter your amount: ")
    amount = int(amount)
    if amount >= 20:
        twe = amount / 20
        amount = amount - twe * 20
            print("You need to pay %d twenty dollar bills" %(twe))
    if amount >= 10:
        ten = amount / 10
        amount = amount - ten * 10
        print("You need to pay %d ten dollar bills" %(ten))
    if amount >= 5:
        five = amount / 5
        amount = amount - five * 5
        print("You need to pay %d five dollar bills" %(five))
    if amount >= 1:
        one = amount / 1
        amount = amount - one * 1
        print("You need to pay %d one dollar bills" %(one))

amt()

当我用一些输入运行它时说 7 我收到这样的错误消息：

Traceback (most recent call last):
  File "dollars.py", line 21, in <module>
    amt()
  File "dollars.py", line 7, in amt
    print("You need to pay %d twenty dollar bills" %(twe))
UnboundLocalError: local variable 'twe' referenced before assignment

为什么 if 语句不能正常工作？即使输入值小于 20 它仍然进入第一个 if 语句

Answer 1

它在视觉上并不明显，但您正在混合制表符和空格。看起来那个 print 语句在里面if，但实际上不是。

这是您的源代码在 Stack Overflow 的文本编辑器中的样子：

Answer 2