python 3.5.1-给用户3尝试无效，然后终止PGM(简单的循环)

Question

我需要帮助（新学生-2周）。我想对此代码进行最小的更改，以使用户3机会输入程序中每个转换的不正确值。输入不正确的值3次后，该程序应终止。唯一的要求是代码必须包含一个循环。我不知道它是需要一个循环还是3个用于循环（每次转换一个）。我尝试了很多场景，似乎无法正确。
谢谢 ！！！！

miles = float(input('Type miles to be converted to km.n')) 
if miles >= 0:
    milesToKm = miles * 1.6 
    print (miles, 'miles is', format(milesToKm, ',.1f'), 'kilometers.n')
    inch = float(input('Give me inches to convert to cm.n')) 
    if inch >=0:
       inchesToCm = inch * 2.54
       print (inch, 'inches is', format(inchesToCm, '.2f'), 'centimeters.n')
       temp = float(input('Give me a Fahrenheit temp to convert to Celsius.n'))
       if temp <= 1000:
          celsius = (temp - 32) * (5/9) 
          print (temp, 'degrees Fahrenheit is', format (celsius, '.1f'), 'Celsius.n')
       else:
          print ('Wrong input, too high.n')               
    else:
        print ('Wrong input, no negatives.n')
else:
    print ('Wrong input, no negatives.n')

我尝试过的一种情况，但不知道如何合并下一个转换或正确地进行。

count = 0
max = 1
for count in range (0, max):
    miles = float (input('Type miles to convert to kilometers?n'))
    if miles >=0:
        max = 1
        milesToKm = miles * 1.6
        print (miles, 'miles is', format(milesToKm, ',.1f'), 'kilometers.n')
        inch = float(input('Give me inches to convert to cm.n'))
    else:
        if max < 3:
            max = max + 1
            print ('Please use a non-negative number, try again.')

谢谢！我根据到目前为止所学到的知识修改了您将您列为所需的格式。（我们尚未学会sys.exit或breaks。）我还必须在最内部循环中插入一个计数= 3，因为PGM仍然希望运行3次，即使有有效的输入。我知道这使用了一个时循环。但是，是否有办法将其作为" for"循环？还是不可能？（希望下面的对齐方式很好，就像我在记事本中对其进行了修改。）

count = 0
while count < 3:
    miles = float(input('Type miles to be converted to km.n')) 
    if miles >= 0:
        milesToKm = miles * 1.6 
        print (miles, 'miles is', format(milesToKm, ',.1f'), 'kilometers.n')
        count = 0:
        while count < 3:
            inch = float(input('Give me inches to convert to cm.n')) 
            if inch >=0:
                inchesToCm = inch * 2.54
                print (inch, 'inches is', format(inchesToCm, '.2f'), 'centimeters.n')
                count = 0:
                while count < 3:
                    temp = float(input('Give me a Fahrenheit temp to convert to Celsius.n'))
                    if temp <= 1000:
                        celsius = (temp - 32) * (5/9) 
                        print (temp, 'degrees Fahrenheit is', format (celsius, '.1f'), 'Celsius.n')
                        count = 3
                    else:
                        print ('Wrong input, too high.n')               
                    count+=1
            else:
                print ('Wrong input, no negatives.n')
            count +=1
    else:
        print ('Wrong input, no negatives.n')
    count +=1   

Answer 1

最简单的您可能是为每个提示符循环，例如以下pseudo python代码：

# Beginning of prompt
i = 0
while i < 3:
    result = float(input(<question>))
    if <isok>:
        print(<result>)
        break
    else:
        print(<error>)
    i += 1
# Three failed inputs.
if i == 3:
    print('Bye, bye!')
    sys.exit(1)

在每个<...>上，您必须为您的程序写一些明智的东西。

update

for循环的变体：

# Beginning of prompt
ok = False
for i in range(3):
    result = float(input(<question>))
    if <isok>:
        print(<result>)
        ok = True
        break
    else:
        print(<error>)
# Three failed inputs.
if not ok:
    print('Bye, bye!')
    sys.exit(1)

请记住ok = False每个for循环之前。

更新2

这是我看到的整个程序，每个输入都可以在其中获得3个机会。我已经自由调整您的print语句。

import sys
# Beginning of prompt
ok = False
for i in range(3):
    miles = float(input('Type miles to be converted to km.n'))
    if miles >= 0:
        milesToKm = miles * 1.6
        print('{} miles is {:.1f} kilometers.'.format(miles, milesToKm))
        ok = True
        break
    else:
        print('Wrong input, no negatives.')
# Three failed inputs.
if not ok:
    print('Bye, bye!')
    sys.exit(1)
# Beginning of prompt
ok = False
for i in range(3):
    inch = float(input('Give me inches to convert to cm.n'))
    if inch >= 0:
        inchesToCm = inch * 2.54
        print('{} inches is {:.2f} centimeters.'.format(inch, inchesToCm))
        ok = True
        break
    else:
        print('Wrong input, no negatives.')
# Three failed inputs.
if not ok:
    print('Bye, bye!')
    sys.exit(1)
# Beginning of prompt
ok = False
for i in range(3):
    temp = float(input('Give me a Fahrenheit temp to convert to Celsius.n'))
    if temp <= 1000:
        celsius = (temp - 32) * (5 / 9)
        print('{} degrees Fahrenheit is {:.1f} Celsius.'.format(temp, celsius))
        ok = True
        break
    else:
        print('Wrong input, too high.')
# Three failed inputs.
if not ok:
    print('Bye, bye!')
    sys.exit(1)
print('All OK')