fuz*_*fle 18 c++ python swig properties
我试图使用swig为某些C++代码创建python绑定.我似乎遇到了一个问题,试图从一些访问器函数创建python属性我有如下方法:
class Player {
public:
void entity(Entity* entity);
Entity* entity() const;
};
我尝试使用python属性函数创建一个属性,但似乎swig生成的包装类与它至少对于setter不兼容.
你如何使用swig创建属性？
Maj*_*cRa 35
有一种简单的方法可以使用swig方法创建python属性.
假设C++代码Example.h:
C++标题
class Example{
public:
void SetX(int x);
int GetX() const;
};
让我们将这个setter和getter转换为python propery'x'.诀窍在.i文件中.我们添加一些"swiggy"内联python代码(带有%pythoncode),它插入到生成的python类的主体中(在自动生成的python代码中).
Swig包装Example.i
%module example
%{
#include "example.h"
%}
class Example{
public:
void SetX(int x);
int GetX() const;
%pythoncode %{
__swig_getmethods__["x"] = GetX
__swig_setmethods__["x"] = SetX
if _newclass: x = property(GetX, SetX)
%}
};
检查python代码:
python测试代码
import example
test = example.Example()
test.x = 5
print "Ha ha ha! It works! X = ", repr(test.x)
这就对了!
无需重写类定义.感谢Joshua的建议,可以使用SWIG指令%extend ClassName {}.
Swig包装Example.i
%module example
%{
#include "example.h"
%}
%extend Example{
%pythoncode %{
__swig_getmethods__["x"] = GetX
__swig_setmethods__["x"] = SetX
if _newclass: x = property(GetX, SetX)
%}
};
可以看出,转换后test.GetX()和test.SetX()仍然存在.人们可以隐藏它们:
a)使用%rename重命名函数,在开头添加'_',从而使python的方法为"private".在SWIG接口.i Example.i中
...
class Example{
%rename(_SetX) SetX(int);
%rename(_GetX) GetX();
...
(%重命名可以放在一些分开的地方,以节省将此类转换为其他语言的可能性,这些语言不需要这些'_')
b)或者可以使用%feature("shadow")
为什么我们必须使用这些东西通过使用SWIG将方法转换为属性？正如所说的,SWIG自私地覆盖_ setattr _,因此必须使用_swig_getmethods_和_swig_setmethods_来注册函数并保持swig方式.
上面列出的方法,特别是PropertyVoodoo的方法......就像烧房子炒鸡蛋一样.它还打破了类布局,因为必须创建继承类以从C++方法生成python属性.我的意思是如果类Cow返回类Milk并且继承的类是MilkWithProperties(Milk),那么如何使Cow生产MilkWithProperties？
这种方法允许人们:
更新 在较新的版本中,SWIG放弃了_swig_property,因此只需使用属性即可.它适用于旧版swig相同.我改变了帖子.
cdi*_*ins 20
在SWIG Lib文件夹中有一个名为"attributes.i"的文件,该文件未在文档中讨论,但包含内联文档.
您所要做的就是将以下行添加到您的接口文件中.
%include <attributes.i>
然后,您将收到许多宏(例如%属性),用于定义现有方法的属性.
摘录来自attributes.i文件中的文档:
以下宏将一对set/get方法转换为"native"属性.当你有一对基本类型的get/set方法时,使用%属性,如:
%attribute(A, int, a, get_a, set_a);
struct A
{
int get_a() const;
void set_a(int aa);
};
哦，这很棘手（也很有趣）。SWIG并不认为这是生成 @property 的机会：我想如果做得不仔细，很容易出错并识别出大量误报。但是，由于 SWIG 不会在生成 C++ 时执行此操作，因此仍然完全可以使用小型元类在 Python 中执行此操作。
因此，下面假设我们有一个 Math 类，可以让我们设置和获取名为“pi”的整数变量。然后我们可以使用这段代码：
#ifndef EXAMPLE_H
#define EXAMPLE_H
class Math {
public:
int pi() const {
return this->_pi;
}
void pi(int pi) {
this->_pi = pi;
}
private:
int _pi;
};
#endif
%module example
%{
#define SWIG_FILE_WITH_INIT
#include "example.h"
%}
[essentially example.h repeated again]
#include "example.h"
class PropertyVoodoo(type):
"""A metaclass. Initializes when the *class* is initialized, not
the object. Therefore, we are free to muck around the class
methods and, specifically, descriptors."""
def __init__(cls, *a):
# OK, so the list of C++ properties using the style described
# in the OP is stored in a __properties__ magic variable on
# the class.
for prop in cls.__properties__:
# Get accessor.
def fget(self):
# Get the SWIG class using super. We have to use super
# because the only information we're working off of is
# the class object itself (cls). This is not the most
# robust way of doing things but works when the SWIG
# class is the only superclass.
s = super(cls, self)
# Now get the C++ method and call its operator().
return getattr(s, prop)()
# Set accessor.
def fset(self, value):
# Same as above.
s = super(cls, self)
# Call its overloaded operator(int value) to set it.
return getattr(s, prop)(value)
# Properties in Python are descriptors, which are in turn
# static variables on the class. So, here we create the
# static variable and set it to the property.
setattr(cls, prop, property(fget=fget, fset=fset))
# type() needs the additional arguments we didn't use to do
# inheritance. (Parent classes are passed in as arguments as
# part of the metaclass protocol.) Usually a = [<some swig
# class>] right now.
super(PropertyVoodoo, cls).__init__(*a)
# One more piece of work: SWIG selfishly overrides
# __setattr__. Normal Python classes use object.__setattr__,
# so that's what we use here. It's not really important whose
# __setattr__ we use as long as we skip the SWIG class in the
# inheritance chain because SWIG's __setattr__ will skip the
# property we just created.
def __setattr__(self, name, value):
# Only do this for the properties listed.
if name in cls.__properties__:
object.__setattr__(self, name, value)
else:
# Same as above.
s = super(cls, self)
s.__setattr__(name, value)
# Note that __setattr__ is supposed to be an instance method,
# hence the self. Simply assigning it to the class attribute
# will ensure it's an instance method; that is, it will *not*
# turn into a static/classmethod magically.
cls.__setattr__ = __setattr__
import example
from util import PropertyVoodoo
class Math(example.Math):
__properties__ = ['pi']
__metaclass__ = PropertyVoodoo
m = Math()
print m.pi
m.pi = 1024
print m.pi
m.pi = 10000
print m.pi
因此，最终结果就是您必须为每个 SWIG Python 类创建一个包装类，然后键入两行：一行用于标记应在属性中转换哪些方法，另一行用于引入元类。