Question

我希望以pythonic方式尽可能接近地复制以下C ++代码，输入和异常处理。我取得了成功，但可能不是我想要的。我本来希望退出程序类似于C ++输入随机字符的方式，在这种情况下它是一个'q'。 while条件下的cin对象不同于make while while的python方式。另外我想知道将2个输入转换为int的简单线是否是一种适当的方法。最后，在python代码中，“再见！”永远不会运行，因为强制应用关闭的EOF（控制+ z）方法。有一些怪癖和整体我很高兴python中需要的代码更少。

额外：如果你看一下最后一个print语句中的代码，那么这是一个很好的方法来打印var和字符串吗？

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);
}

的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，并在a等于-b时引发异常：

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，方法format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投射到except时引发ValueError，您可能希望使用int阻止。

Answer 2

这是我要向你抛出的一段代码。类似的东西在C ++中并不容易实现，但它通过分离关注点在Python中使事情变得更加清晰：

# so-called "generator" function
def read_two_numbers():
    """parse lines of user input into pairs of two numbers"""
    try:
        l = raw_input()
        x, y = l.split()
        yield float(x), float(y)
    except Exception:
        pass

for x, y in read_two_numbers():
    print('input = {}, {}'.format(x, y))
print('done.')

它使用一个所谓的生成器函数，它只处理输入解析以将输入与计算分开。这不是“尽可能接近”，而是你所要求的“以pythonic方式”，但我希望你会发现它仍然有用。此外，我冒昧地使用浮点数而不是整数来表示数字。

还有一件事：升级到Python 3，版本2不再开发，只是接收错误修正。如果您不依赖于仅适用于Python 2的任何库，那么您应该感觉不太大。

Python输入和异常与C ++

2 个答案: