Python 无效语法：Print 和 Elif 语句

Question

我对 Python 和编程真的很陌生（准确地说是 2 天）。我在闲置时试图想出一个比 print "Hello world." 更复杂的过程我想知道你们中是否有人能告诉我为什么它将我的 print 和 elif 语句标记为无效。我正在使用 Python 2.7.10，谢谢！

A = raw_input("Do you live in the US or Canada?")
if A == " US" or "Canada":
        print "Welcome!"
else:
    print "We're sorry, but your country is currently not supported!"

B = int(raw_input("How much is your package?")
        if B >= 25
            print "Your shipping is .00"
    elif B >= 50
        print "Your shipping is .00"
else:
    print "Congrats, your shipping is free!"

Answer 1

已为您修复:)。看看有什么不同，你会学到的，小学徒：

A = raw_input("Do you live in the US or Canada?")

if A == "US" or A == "Canada":
    print "Welcome!"
else:
    print "We're sorry, but your country is currently not supported!"

B = float(raw_input("How much is your package?"))

if B >= 25:
    print "Your shipping is .00"
elif B >= 50:
    print "Your shipping is .00"
else:
    print "Congrats, your shipping is free!"

Answer 2

您注意到 python 的第一件事可能是一致的缩进不仅是个好主意，而且是强制性的。有经验的程序员，不管他们是否写 Python ，总是会这样做，所以这没什么大不了的。使用空格（4 个是标准）并避免使用制表符 - 更改您的编辑器以用 4 个空格替换制表符。

因为四舍五入，所以在金额上使用浮点数是个坏主意。最好使用大类型，如 Decimal，或将金额存储为以分为单位的 int，然后在显示时插入小数点。为简单起见，我坚持使用 float，但请注意。

您的代码中有很多逻辑错误，还有样式问题。编程风格不仅仅是关于什么看起来好看，而是当你回过头来时是否能理解你的代码。

风格点：

不要对变量使用大写。按照惯例，大写字母保留给常量

使用有意义的变量名，而不是 A 和 B

这是一个更正的程序，带有注释。请阅读评论！ :

# This is a comment, it is ignored by python
# This is used later on by sys.exit()
import sys

# Logically the user would enter "Yes" or "No" to this quesion,
# not US or Canada!
ans = raw_input("Do you live in the US or Canada? ")    # Notice the space after ?

# Note how the condition has been expanded
if ans == "US" or ans == "Canada":
    print "Welcome!" 
else: 
    print "We're sorry, but your country is currently not supported!"

    # Now what?  Your program just carried on.  This will stop it
    sys.exit()

# I'm using a floating point number for simplicity
amount = float(raw_input("How much is your package? "))

# I changed this around, since 50 is also >= 25!
# However, this is strange.  Usually the more you spend the LESS the shipping!
# You were missing the : after the condition
if amount >= 50:
    print "Your shipping is .00"
    amount += 8           # This adds 8 to the amount
elif amount >= 25:
    print "Your shipping is .00"
    amount += 4           # This adds 4 to the amount
else:
    print "Congrats, your shipping is free!"

# print the amount showing 2 decimal places, rounding
print "Amount to pay: $%.2f" % (amount)

你还有很多事要做。也许应对用户为国家名称输入小写或混合大小写字母 - 并问问自己这个问题对用户来说是否合乎逻辑。

稍后您可能想要一个有效国家/地区列表，并使用 in 来测试用户是否输入了有效国家/地区。然后将其扩展为使用字典，指示每个国家/地区的货币符号、运费和货币兑换率。

享受Python！

Python 无效语法：Print 和 Elif 语句

Python Invalid Syntax: Print and Elif statements

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