在python中使用while检查时出错

Question

while True:
    self.soil_type = input("Please choose soil type - alkaline, neutral, acidic: ")
    print('-'*30)
    print('')
    if self.soil_type != "alkaline" and "neutral" and "acidic":
        print("***NOT A VALID SOIL TYPE***")
        continue
    else:
        False

我想用while循环进行错误检查。 如果我键入的不是碱性、中性、酸性，请打印“不是有效的土壤类型”，然后继续输入命令。如果我键入了一种正确的土壤类型，请退出循环并转到下一步。你知道吗

但没用。即使我输入了正确的一个（例如“酸性”），它显示“不是一个有效的土壤类型”。我错过了什么？：）

Answer 1

您使用的if条件是错误的。你知道吗

应该是这样的-

while True:
    self.soil_type = input("Please choose soil type - alkaline, neutral, acidic: ")
    print('-'*30)
    print('')
    if (self.soil_type != "alkaline") and (self.soil_type != "neutral") and (self.soil_type != "acidic"):
        print("***NOT A VALID SOIL TYPE***")
        continue
    else:
        False

原因是你把它说成-

if <condition> and "neutral" and "acidic":
     ...

因为“中性”和“酸性”只是真值，如果不是碱性，第一个条件就是真的。这使得整个情况属实，它只是打印-

***NOT A VALID SOIL TYPE***

希望这有帮助。你知道吗

Answer 2

如果您选择if something，那么您的代码将更可读，而不是选择if not something：

while True:
    self.soil_type = input("Please choose soil type - alkaline, neutral, acidic: ")
    print('-'*30)
    print('')
    if self.soil_type == "alkaline" or self.soil_type == "neutral" or self.soil_type == "acidic":
      print("**VALID**")
      print self.soil_type
      break
    else:
      print("***NOT A VALID SOIL TYPE***")

提醒（布尔代数）：

The rules can be expressed in English as:

• the negation of a disjunction is the conjunction of the negations; and

• the negation of a conjunction is the disjunction of the negations; or

• the complement of the union of two sets is the same as the intersection of their complements; and

• the complement of the intersection of two sets is the same as the union of their complements.

or

not (A or B) = not A and not B; 
and
not (A and B) = not A or not B

https://en.wikipedia.org/wiki/De_Morgan%27s_laws

Answer 3

while True:
    self.soil_type = input("Please choose soil type - alkaline, neutral, acidic: ")
    print('-'*30)
    print('')
    if not(self.soil_type == "alkaline" or self.soil_type == "neutral" or self.soil_type == "acidic"):
        print("***NOT A VALID SOIL TYPE***")
        continue
    else:
        break

试着用这个……应该有用！你知道吗