Python 不正确的 Output 使用 float() [重复]

Question

这个问题在这里已经有了答案：

为什么“a == x or y or z”总是计算为 True？ 我如何将“a”与所有这些进行比较？ (6 个回答)

5 小时前关闭。

我正在尝试计算形状面积和周长，然后比较它们。 例如，如果我想得到长度 = 5 的正方形的面积，那么我希望面积 = 长度 * 长度 = 5 * 5 = 25。但是，我得到的答案完全不同，我不确定为什么。 我在 Python 中的计算有什么问题？

import math
pi = 3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651328230664709384460955058223172535940812848111745028410270193852110555964462294895

shape1 = input('What is your first shape? ')
length1 = input("What is the length of its side? ")
shape2 = input("What is your second shape? ")
length2 = input("What is the length of its side? ")

#Equate shape1 area and perimeter
if shape1 == 'Triangle' or 'triangle':
    shape1 = float(3)
    area1 = ((math.sqrt(3)/float(4))*float(length1)*float(length1))
    perimeter1 = float(length1) * float(3)
elif shape1 == 'Square' or 'square':
    shape1 = float(4)
    area1= float(length1) * float(length1)
    perimeter1 = float(length1)*4
elif shape1 == 'Hexagon' or 'hexagon':
    shape1 = float(6)
    area1 = (((3*(math.sqrt(3)))/2)*length1*length1)
    perimeter1 = float(length1) * float(6)
#Equate shape2 area and perimeter
if shape2 == 'Triangle' or 'triangle':
    shape2 = float(3)
    area2 = ((math.sqrt(3)/float(4))*float(length2)*float(length2))
    perimeter2 = float(length2) * float(3)
elif shape2 == 'Square' or 'square':
    shape2 = float(4)
    area2 = float(length2) * float(length2)
    perimeter2 = float(length2) * float(4)
elif shape2 == 'Hexagon' or 'hexagon':
    shape2 = float(6)
    area2 = (((3*(math.sqrt(3)))/float(2))*float(length2)*float(length2))
    perimeter2 = float(length2) * float(6)

#Compare area values and print
if float(area1) > float(area2):
    print("Polygon 1's area is larger")
    print(float(area1), float(area2))
elif area1 == area2:
    print("The areas are equal")
    print(float(area1), float(area2))
else:
    print ("Polygon 2's area is larger")
    print(float(area1), float(area2))

#Compare perimeter values and print
if float(perimeter1) > float(perimeter2):
    print("Polygon 1's perimeter is larger")
    print(float(perimeter1), float(perimeter2))
elif float(perimeter1) == float(perimeter2):
    print("The perimeters are equal")
    print(float(perimeter1), float(perimeter2))
else:
    print ("Polygon 2's perimeter is larger")
    print(float(perimeter1), float(perimeter2))

示例 output

What is your first shape? square
What is the length of its side? 5.5
What is your second shape? triangle
What is the length of its side? 3
Polygon 1's area is larger
13.098634232239634 3.897114317029974
Polygon 1's perimeter is larger
16.5 9.0

Process finished with exit code 0

Answer 1

if shape1 == 'Triangle' or 'triangle':

麻烦的是，这被解析为(shape1 == 'Triangle') or ('triangle') ，然后字符串'triangle'不为空，所以它被认为是真的，所以整个 if 语句都是真的。

这应该是

if shape1 == 'Triangle' or shape1 == 'triangle':

或者更好，

if shape1 in ('Triangle', 'triangle'):

甚至更好：

if shape1.lower() == 'triangle':

另请参阅如何针对单个值测试多个变量是否相等？