input（）：“ NameError：未定义名称'n'”

Question

好的，所以我正在用python编写成绩检查代码，我的代码是：

unit3Done = str(input("Have you done your Unit 3 Controlled Assessment? (Type y or n): ")).lower()
if unit3Done == "y":
    pass
elif unit3Done == "n":
    print "Sorry. You must have done at least one unit to calculate what you need for an A*"
else:
    print "Sorry. That's not a valid answer."

当我通过python编译器运行它并选择时"n"，出现一条错误消息：

“ NameError：未定义名称’n’”

当我选择"y"我再NameError有'y'是问题，但是当我做别的事情，代码运行正常。

任何帮助是极大的赞赏，

谢谢。

Answer 1

raw_input在Python
2中使用来获取字符串，input在Python
2中等效于eval(raw_input)。

>>> type(raw_input())
23
<type 'str'>
>>> type(input())
12
<type 'int'>

因此，当您输入类似的内容时n，input它会认为您正在寻找一个名为的变量n：

>>> input()
n
Traceback (most recent call last):
  File "<ipython-input-30-5c7a218085ef>", line 1, in <module>
    type(input())
  File "<string>", line 1, in <module>
NameError: name 'n' is not defined

raw_input 工作良好：

>>> raw_input()
n
'n'

帮助raw_input：

>>> print raw_input.__doc__
raw_input([prompt]) -> string

Read a string from standard input.  The trailing newline is stripped.
If the user hits EOF (Unix: Ctl-D, Windows: Ctl-Z+Return), raise EOFError.
On Unix, GNU readline is used if enabled.  The prompt string, if given,
is printed without a trailing newline before reading.

帮助input：

>>> print input.__doc__
input([prompt]) -> value

Equivalent to eval(raw_input(prompt)).