python - 如何使 float 在 python 3 中具有特定范围(或者我可以)？

Question

我一直在尝试让这个程序运行，并且它可以运行，但是一旦我让它运行，我就发现了这个问题。现在，它会要求 GradePoint 和学时，并按预期打印出 GPA，但我可以在 GradePoint 中输入任何内容，它会输出一个值。我想要的是 GradePoint 仅在用户输入 0.0-4.0 之间的数字时才起作用。 我正在考虑某种循环，例如 if 循环，但是有没有更简单的方法(或首选方法)来做到这一点？

代码如下:

def stu():
stu = Student

class Student:
def __init__(self, name, hours, qpoints):
    self.name = name
    self.hours = float(hours)
    self.qpoints = float(qpoints)

def getName(self):
    return self.name

def getHours(self):
    return self.hours

def getQpoints(self):
    return self.qpoints

def getStudent(infoStr):
    name, hours, qpoints = infoStr.split("\t")
    return Student(name, hours, qpoints)

def addGrade(self, gradePoint, credits):
    self.qpoints = gradePoint * credits
    self.hours = credits
    self.gradePoint = float(gradePoint)
    self.credits = float(credits)

def gpa(self):
    return self.qpoints/self.hours

def main():
stu = Student(" ", 0.0, 0.0)
credits = int(input("Enter Credit Hours "))
gradePoint = float(input("Enter Grade Point"))
if gradePoint > 4.0:
        print("Please enter a Grade Point that is less then 4.")
stu.addGrade(gradePoint,credits)
output = stu.gpa()
print("\nStudent GPA is: ", output)


main()

这是 shell 打印输出(我知道成绩点在 GPA 中重复，这是针对一个类(class)的，我们应该使用一个骨架程序并更改一些东西):

Enter Credit Hours 4
Enter Grade Point 3.5
Student GPA is:  3.5

Enter Credit Hours 12
Enter Grade Point 3.2
Student GPA is:  3.2

谢谢!

编辑:我只是按照评论中的建议做了一个 if 循环，它在某种程度上起到了作用，因为它打印出了我想要的内容，但没有让它停止并等待正确的输入。我不太确定如何让它做到这一点。

这是来自 shell 的新打印内容:

Enter Credit Hours 4
Enter Grade Point 3.5
Student GPA is:  3.5

Enter Credit Hours 4
Enter Grade Point 4.5
Please enter a Grade Point that is less then 4.
Student GPA is:  4.5

Answer 1

您可以检查用户输入是否满足您的要求，如果不满足则抛出异常。这将使程序记录一条错误消息并在无效的用户输入时停止。

最基本的方法是使用断言语句:

def main():
    stu = Student(" ", 0.0, 0.0)
    credits = int(input("Enter Credit Hours "))
    assert credits > 0 and credits < 4, "Please enter a number of Credit Hours between 0 and 4."

如果您希望应用程序不断提示用户直到输入有效输入，则至少需要一个 while 循环。

例如:

def main():
    stu = Student(" ", 0.0, 0.0)
    while True:
        credits = int(input("Enter Credit Hours "))
        if credits > 0 and credits < 4:
            break
        else:
            print("Please enter a number of Credit Hours between 0 and 4")

    while True:
        gradePoint = float(input("Enter Grade Point"))
        if gradePoint <= 4.0:
            break
        else:
            print("Please enter a Grade Point that is less then 4.")

    stu.addGrade(gradePoint,credits)
    output = stu.gpa()
    print("\nStudent GPA is: ", output)