python - 为什么我的 "if"语句在 python 中不起作用？

Question

这个问题已经有答案了:

Check if numbers are in a certain range in python (with a loop)? [duplicate] (3 个回答)

已关闭 4 年前。

我想知道为什么我的“if”语句不起作用。我被要求提供输入，但之后什么也没有发生。它不会打印出它是A、B、C还是D。

def main():
    printLetterGradeFromNumber(input("The grade as a number: "))

def printLetterGradeFromNumber(number_grade):

    A = range(90, 100)
    B = range(80, 89)
    C = range(70, 79)
    D = range(60, 69)

    if number_grade == A:
         print("That student gets an A")
    elif number_grade == B:
        print("That student gets a B")
    elif number_grade == C:
        print("That student gets a C")
    elif number_grade == D:
        print("That student gets a D")

    return number_grade


main()

Answer 1

有两个问题:

• input ，里面main ，需要转换为 int
  • 目前，input是 str ，这永远不会是True当测试 A 内的成员资格时, B , C或D
  • 示例:'90' == 90比较为False ，所以'90' in A是 False
• 使用membership operator, in ，而不是 comparison operator, == .

def main():
    printLetterGradeFromNumber(int(input("The grade as a number: ")))

def printLetterGradeFromNumber(number_grade):
    A = range(90, 100)
    B = range(80, 89)
    C = range(70, 79)
    D = range(60, 69)

    if number_grade in A:
         print("That student gets an A")
    elif number_grade in B:
        print("That student gets a B")
    elif number_grade in C:
        print("That student gets a C")
    elif number_grade in D:
        print("That student gets a D")

    return number_grade

main()

输出:

The grade as a number:  90
That student gets an A

替代实现:

• Don’t Forget NumPy!
• numpy.digitize
  • digitize返回 index的value ，在bins内。 value < 60返回index = 0 ，而value >= 90返回index = 4 .
  • 使用 index 找到字母等级的grades 。因此，顺序为 grades必须对应于bins .

from numpy import digitize

def print_letter_grade():
    value = int(input('The grade as a number: '))
    grades = ['F', 'D', 'C', 'B', 'A']
    index = digitize(value, bins=[60, 70, 80, 90])
    print(f'The student gets an {grades[index]}')