c++ - Python 输入和异常与 C++

Question

我想以 pythonic 方式复制以下 C++ 代码，其中输入和异常处理尽可能接近。我取得了成功，但可能不是我想要的。我希望退出程序类似于输入随机字符的 C++ 方式，在本例中它是一个“q”。 while 条件中的 cin 对象不同于使 while 为 True 的 python 方式。我还想知道将 2 个输入转换为 int 的简单行是否是一种合适的方法。最后，在 python 代码中，“再见!”永远不会运行，因为 EOF (control+z) 强制应用程序关闭的方法。有一些怪癖，总的来说，我对 python 中需要的代码更少感到满意。

额外:如果您查看最后一个 print 语句中的代码，这是同时打印 var 和 strings 的好方法吗？

欢迎任何简单的技巧/提示。

C++

#include <iostream>

using namespace std;

double hmean(double a, double b);  //the harmonic mean of 2 numbers is defined as the invese of the average of the inverses.

int main()
{
    double x, y, z;
    cout << "Enter two numbers: ";

    while (cin >> x >> y)
    {
        try     //start of try block
        {
            z = hmean(x, y);
        }           //end of try block
        catch (const char * s)      //start of exception handler; char * s means that this handler matches a thrown exception that is a string
        {
            cout << s << endl;
            cout << "Enter a new pair of numbers: ";
            continue;       //skips the next statements in this while loop and asks for input again; jumps back to beginning again
        }                                       //end of handler
        cout << "Harmonic mean of " << x << " and " << y
            << " is " << z << endl;
        cout << "Enter next set of numbers <q to quit>: ";
    }
    cout << "Bye!\n";

    system("PAUSE");
    return 0;
}

double hmean(double a, double b)
{
    if (a == -b)
        throw "bad hmean() arguments: a = -b not allowed";
    return 2.0 * a * b / (a + b);
}

python

class MyError(Exception):   #custom exception class
    pass

def hmean(a, b):
    if (a == -b):
        raise MyError("bad hmean() arguments: a = -b not allowed")  #raise similar to throw in C++?
    return 2 * a * b / (a + b);

print "Enter two numbers: "

while True:
    try:
        x, y = raw_input('> ').split() #enter a space between the 2 numbers; this is what .split() allows.
        x, y = int(x), int(y)   #convert string to int
        z = hmean(x, y)
    except MyError as error:
        print error
        print "Enter a new pair of numbers: "
        continue

    print "Harmonic mean of", x, 'and', y, 'is', z, #is this the most pythonic way using commas? 
    print "Enter next set of numbers <control + z to quit>: "   #force EOF

#print "Bye!" #not getting this far because of EOF

Answer 1

对于函数 hmean 我会尝试执行 return 语句，如果 a 等于 -b 则引发异常:

def hmean(a, b):
    try:
        return 2 * a * b / (a + b)
    except ZeroDivisionError:
        raise MyError, "bad hmean() arguments: a = -b not allowed"

要在字符串中插入变量，format 方法是一种常见的替代方法:

print "Harmonic mean of {} and {} is {}".format(x, y, z)

最后，如果在将 x 或 y 转换为 int 时出现 ValueError，您可能希望使用 except block 。