如何让用户重用python计算器中先前计算的结果 [英] How to let the user reuse a result from the previous computation in a python calculator

问题描述

我是python的新手，所以我对此不太了解。我做了一个计算器，我希望它接受：

I am fairly new at python so I don't know much about it. I made a calculator and I want it to accept a:

ans()

输入。当前，如果没有[0-9 * /-+]以外的内容，有一部分可以阻止程序执行输入，因此不会崩溃。我该怎么做

input. Currently, there is a part that stops the program from executing an input if there is something other than [0-9 */-+] so it does not crash. How can I make

ans()

表示上次输入的方程式的输出，因此我可以输入以下内容：

represent the output of the equation last entered so I can enter something like this:

>> 8*8 #last input
64 #last output
>> ans()*2 #current input
128 # current output

希望我能正确解释所有内容这是我的代码：

Hopefully I explained everything correctly and here is my code:

valid_chars = "0123456789-+/* \n";
while True:
x = "x="
y = input(" >> ")
x += y
if any(c not in valid_chars for c in y):
    print("WARNING: Invalid Equation")
    continue
try:
    exec(x)
except (SyntaxError, ZeroDivisionError):
    print ("WARNING: Invalid Equation")
else:
    print(x)

更新：我添加了在答案中建议的几行，但它没有运行（我也修复了缩进）：

Update: I added several lines that were recommended in the answers but it would not run (I also fixed the indents):

valid_chars = "0123456789-+/* \n";
while True:
    x = "x="
    y = input(" >> ")
    x += y
    def ans():
        return _
    def ans():
        try:
            return _
    except NameError:
        return 0 # appropriate value
    if any(c not in valid_chars for c in y):
        print("WARNING: Invalid Equation")
        continue
    try:
        exec(x)
    except (SyntaxError, ZeroDivisionError):
        print ("WARNING: Invalid Equation")
    else:
        print(x)

错误：除了NameError之外，意外缩进

Error: "Unexpected Indent" for except NameError

我做错了什么以及如何解决？谢谢

What did I do wrong and how can I fix this? Thanks

推荐答案

如果要在python解释器中使用程序，可以使用一个简单的技巧。解释器将最后的输出存储在特殊变量 _ 中：

If you want to use your program in the python interpreter, you can use a simple trick. The interpreter stores the last output in the special variable _:

>>> def ans():
...     return _
... 
>>> 8 * 8
64
>>> ans() * 8
512
>>> def ans():
...     return _
... 
>>> 8 * 8
64
>>> ans() * 2
128
>>> 

请记住， _ 可以提高 NameError 如果到目前为止没有任何输出。您可以使用类似的方法处理它：

Just remember, that _ can raise a NameError if there hasn't been any output so far. You can handle it with something like that:

>>> def ans():
...     try:
...         return _
...     except NameError:
...         return 0 # appropriate value
... 

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