扩展modu中用户定义Python类的Python-to-Python_转换器

Question

< P> >我想返回下面的Python类的实例，它模仿了我的C++扩展模块：/P>>三状态逻辑的Booo:：TrBooL

class Tribool(object):

def __init__(self, value = None):
    if any(value is v for v in (False, True, None)):
        self.value = value
    else:
        raise ValueError("Tribool must be False, True or None")

def __nonzero__(self):
    raise TypeError("Tribool may not be used as an implicit bool")

def __eq__(self, other):
    if isinstance(other, Tribool):
        return self.value is other.value
    if any(other is v for v in (False, True, None)):
        return self.value is other
    raise TypeError("Tribool can only be compared to another Tribool or False, True, or None")

def __ne__(self, other):
    return not (self == other)

def __invert__(self):
    if self.value is False:
        return Tribool(True)
    elif self.value is True:
        return Tribool(False)
    elif self.value is None:
        return Tribool(None)
    raise ValueError("Tribool must be False, True or None")

def __and__(self, other):
    if (self.value is False) or (other.value is False):
        return Tribool(False)
    if (self.value is None) or (other.value is None):
        return Tribool(None)
    return Tribool(True)

def __or__(self, other):
    if (self.value is True) or (other.value is True):
        return Tribool(True)
    if (self.value is None) or (other.value is None):
        return Tribool(None)
    return Tribool(False)

def __xor__(self, other):
    if (self.value is None) or (other.value is None):
        return Tribool(None)
    if self == other:
        return Tribool(False)
    return Tribool(True)

def __str__(self):
    if any(self.value is v for v in (False, True, None)):
        return str(self.value)
    raise ValueError("Tribool must be False_, True_ or Maybe_")

def __repr__(self):
    return "Tribool(%s)" % str(self)

我认为我需要编写一个to_python_转换器，但我无法想出如何为用户定义的python类型编写转换器。我已经阅读了boostpython文档，并使用Google进行了搜索，但没有找到一个好的示例。感谢任何帮助。在

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更新：

以下C++代码将将TRIPBOL转换为Python值TRUE、FALSE和NORE，这是部分解决方案：

^{pr2}$

我无法理解的部分是如何返回纯Python Tribool类的实例，而不是从转换例程返回值True、False和None。在

Answer 1

这可以用与从Python方法返回Tribool相同的方式完成。在这两种语言中，都需要获得TriboolPython类对象的句柄，然后调用它。返回的对象将是Tribool类型的实例。在

例如：

from tribool import Tribool
x = Tribool(False)

相当于：

^{pr2}$

---

下面是一个简化的例子，其中用户定义的Python模块（^ {CD4>}）包含Python类（^ {CD5>}），而C++ Python扩展模块（^ {CD6>}）提供了一个^ {CD7>}函数，创建了^ {CD8>}对象。在

spam.pyPython模块：

class Spam(object):

    def __init__(self, value):
        self.value = value

    def __str__(self):
        return self.__repr__() + " has a value of " + str(self.value)

example.cpp扩展模块：

#include <boost/python.hpp>

boost::python::object make_spam(boost::python::object value)
{
  // from spam import Spam
  // return Spam(value)
  return boost::python::import("spam").attr("Spam")(value);
}

BOOST_PYTHON_MODULE(example)
{
  boost::python::def("make_spam", &make_spam);
}

交互式Python：

>>> import example
>>> print example.make_spam(False)
<spam.Spam object at 0xb74be1ac> has a value of False
>>> print example.make_spam(True)
<spam.Spam object at 0xb74be10c> has a value of True
>>> print example.make_spam(None)
<spam.Spam object at 0xb74be1ac> has a value of None