Python始终得到相同结果

Question

我下面写的程序有以下要求：

# Design a program that prompts the user to enter the names of two primary colors
# to mix.  If the user enters anything other than red, blue or yellow, the
# program should display an error message.  Otherwise the program should display 
# the name of the secondary color that results.

这是我写的代码——基于我之前写的一个Java程序，结果显然在Python中完全不对：

print('You will be mixing two primary colors to get a resulting color.')
print('Primary colors are blue, red and yellow \n')

red = False
blue = False
yellow = False

color1 = bool(input('Enter your first primary color: \n'))
color2 = bool(input('Enter your second primary color: \n'))

if color1 == red and color2 == blue:
        print('That makes purple!')

elif color1 == blue and color2 == red:
        print('That makes purple!')

elif color1 == yellow and color2 == red:
    print('That makes orange!')

elif color1 == red and color2 == yellow:
    print('That makes orange!')

elif color1 == blue and color2 == yellow:
    print('That makes green!')

elif color1 == yellow and color2 == blue:
    print('That makes green!')

else:
    print('You did not enter a primary color!')

无论我输入什么颜色组合，结果总是“这会变成紫色！”我在这个程序的逻辑上哪里出错了？此外，当我没有输入绿色作为主色时，我得到的是：

Traceback (most recent call last):
File "color.py", line 19, in <module>
color1 = bool(input('Enter your first primary color: \n'))
File "<string>", line 1, in <module>
NameError: name 'green' is not defined

而不是错误信息“你没有输入主色！”

我哪里出错了？

编辑：这是我新的代码，除了报错之外，其他都能正常工作。

print('You will be mixing two primary colors to get a resulting color.')
print('Primary colors are blue, red and yellow \n')

red = 1
blue = 2
yellow = 3

color1 = input('Enter your first primary color: \n')
color2 = input('Enter your second primary color: \n')

if color1 == 1 and color2 == 2:
    print('That makes purple!')

elif color1 == 2 and color2 == 1:
    print('That makes purple!')

elif color1 == 3 and color2 == 1:
print('That makes orange!')

elif color1 == 1 and color2 == 3:
print('That makes orange!')

elif color1 == 2 and color2 == 3:
print('That makes green!')

elif color1 == 3 and color2 == 2:
print('That makes green!')

else:
print('You did not enter a primary color!')

Answer 1

问题似乎出在这些代码行上：

red = False
blue = False
yellow = False

color1 = bool(input('Enter your first primary color: \n'))
color2 = bool(input('Enter your second primary color: \n'))

当你输入一个颜色时，不管你输入的是哪个颜色，程序都会把它设置为假（false）。我用红色和黄色来举例说明：

color1 = bool(red)

因为你之前把红色定义为假：

color1 = bool(False)
color1 = False

同样，

color2 = bool(yellow)

黄色也被定义为假。

color2 = bool(False)
color2 = False

所以当我们到达你的第一个条件判断时，

if color1 == red and color2 == blue:

计算机看到的是：

if False==False and False == False:

这会被判断为真（true）。

if True and True:
if True:

你遇到的问题部分可能是因为你使用了input()。对于Python 2.x（我假设你在用这个版本），input()会对输入的内容进行评估。例如：

input("Enter Something")
>>>3
input("Enter Something Else")
>>>3.1

这会分别返回整数值3和浮点值3.1。计算机会查看你输入的内容，并尽力给你一个有意义的数据。在你的情况下，

yellow = False

color1 = bool(input('Enter your first primary color: \n'))

>>>yellow

计算机会在程序的命名空间中查找表达式黄色的值，而在这个程序中，黄色的值是假的。

你可以尝试使用raw_input()，它不会评估输入的内容，而是简单地返回你输入的字符串值。例如：

input()
>>>yellow

这会评估为假，但

raw_input()
>>>yellow

这会评估为字符串值“黄色”。

尝试把你的颜色常量定义为字符串，而不是布尔值（bool），并且处理输入时也当作字符串来处理。所以，

yellow = "yellow"

而不是

yellow = False

Answer 2

你的代码有一些大问题。首先，你调用了bool(input())。只要你输入了任何内容，color1和/或color2就会被设置为True。

所以，你实际上是在执行if True == False... 你的代码并没有检查颜色的实际名称。相反，我建议你直接使用input()来获取一个字符串。

这是你修改后的代码：

print('You will be mixing two primary colors to get a resulting color.')
print('Primary colors are blue, red and yellow \n')

color1 = input('Enter your first primary color: \n')
color2 = input('Enter your second primary color: \n')

if color1 == 'red' and color2 == 'blue':
        print('That makes purple!')

elif color1 == 'blue' and color2 == 'red':
        print('That makes purple!')

elif color1 == 'yellow' and color2 == 'red':
    print('That makes orange!')

elif color1 == 'red' and color2 == 'yellow':
    print('That makes orange!')

elif color1 == 'blue' and color2 == 'yellow':
    print('That makes green!')

elif color1 == 'yellow' and color2 == 'blue':
    print('That makes green!')

else:
    print('You did not enter a primary color!')

Answer 3

color1 = bool(input('Enter your first primary color: \n'))

如果我们把这个简化一下，我们得到

color1 = bool("red") #color1 becomes True

所以现在你的比较是在判断 False 是否等于 True - 完全忽略了你输入的颜色。

试试这样的

RED = 'red'
BLUE = 'blue'

color1 = input('Enter your first primary color: \n').lower()
color2 = input('Enter your second primary color: \n').lower()

if color1 == RED and color2 == BLUE:
    print('That makes purple!')

Answer 4

你的问题出现在这些代码行：

color1 = bool(input('Enter your first primary color: \n'))
color2 = bool(input('Enter your second primary color: \n'))

当你这样做时，任何非空的输入值都会返回 True。你唯一能得到 False 的方法就是在提示符下直接按 return 键，提交一个空字符串。你处理用户输入的逻辑有点问题。你可能想要：

if color1 == 'red'

在你去掉多余的 bool 调用之后，不过这只是个建议。

Answer 5

你应该把 color1 和 color2 跟字符串进行比较，而不是跟布尔值比较：

color1 = input('Enter your first primary color: \n')
color2 = input('Enter your second primary color: \n')
if color1 == "red" and color2 == "blue":
    print("That makes purple!")