为什么它总是生成True？

Question

该程序应该解决转换不同长度单位的问题。由于某种原因，该程序只响应第一个＆＃34; if＆＃34;声明并运行＆＃34; meters_to_inches＆＃34;和＆＃34;米_to_centimeters＆＃34;仅用于功能，即使用户输入它们有英寸或厘米。如果用户输入＆＃34;米＆＃34;然后是长度，它返回它应该的东西，即以英寸和厘米为单位的长度。但是如果用户想要从英寸或厘米转换，它仍然使用米功能的数学并且不采用elif语句。有人可以帮助我吗？

#Title
print "Length Conversion"


#Description
print "This application will calculate the conversion of different units of length. There will be different conversion factors as described in the application."
print '\n'

#Directions
print "Hello. This application will help you convert into different units of lenth."
print '\n'
#Question
print "These are the different units to convert to and from:"
list = ["-Meters", "-Inches", "-Centimeters"]
for unit in list:
    print unit
print '\n'
#Question
units = raw_input("Which of these units do you have and would like to convert to one or both of the other two?")
print '\n'
amount = int(raw_input("How much of it do you have?"))
#Functions. One of these functions converts meters to inches, and the other converts meters to centimers. The original input gets muultiplied or divided by a certain number in order for it to be converted.
def meters_to_inches(amount):
  number = amount / 0.0254
  return number
def meters_to_centimeters(amount):
  number = amount * 100
  return number
#Functions. One of these functions converts inches to meters, and the other converts inches to centimers. The original input gets muultiplied or divided by a certain number in order for it to be converted.
def inches_to_meters(amount):
  number = amount * 0.0254
  return number
def inches_to_centimeters(amount):
  number = amount * 2.54
  return number
#Functions. One of these functions converts centimeters to meters, and the other converts centimeters to inches. The original input gets muultiplied or divided by a certain number in order for it to be converted.
def centimeters_to_meters(amount):
  number = amount / 100
  return number
def centimeters_to_inches(amount):
  number = amount / 2.54
  return number

if units == "Meters" or "meters":
  print meters_to_inches(amount)
  print "(inches)"
  print'\n'
  print meters_to_centimeters(amount)
  print "(centimeters)"
elif units == "Inches" or "inches":
  print inches_to_meters(amount)
  print "(meters)"
  print'\n'
  print inches_to_centimeters(amount)
  print "(centimeters)"
elif units == "Centimeters" or "centimeters":
  print centimeters_to_inches(amount)
  print "(inches)"
  print '\n'
  print centimeters_to_meters(amount)
  print "(meters)"
else:
  print "The unit you have given does not match a conversion this application provides"

Answer 1

你的条件不对。

以下条件将始终在Python中生成True：

if variable == 'value' or 'other-value'

我的猜测是你打算这样做：

if variable == 'value1' or variable == 'value2'`

因此，使用upper或lower字符串的方法来避免这些or。例如，

if unit.upper() == 'INCHES'

为什么它总是生成True？

如果您执行以下代码：

if 2:
    print 'yes!'
if 0:
    print 'no!'

您将看到Python仅打印yes!。这意味着Python中除0之外的任何数字的布尔表达式都是True。现在，因为您知道or用于分隔两个布尔表达式，然后使用此if-statement：

if x == 3 or 2

您知道2是True，因为在使用True执行代码行时，其中一个布尔表达式为or就足够了与该陈述有关。

为什么此代码无法正常工作？不接受elif陈述

1 个答案:

为什么它总是生成True？