Python方法解析之谜 [英] Python method resolution mystery

问题描述

我不知道为什么该程序失败.

I can't figure out why this program is failing.

#!/usr/bin/env python
from __future__ import division, print_function
from future_builtins import *
import types
import libui as ui
from PyQt4 import QtCore
import sip

p = ui.QPoint()
q = QtCore.QPoint()

def _q_getattr(self, attr):
    print("get %s" % attr)
    value = getattr(sip.wrapinstance(self.myself(), QtCore.QPoint), attr)
    print("get2 %s returned %s" % (attr, value))
    return value

p.__getattr__ = types.MethodType(_q_getattr, p)

print(p.__getattr__('x')())  # Works!  Prints "0"
print(p.x())  # AttributeError: 'QPoint' object has no attribute 'x'

我使用Boost.Python创建了libui，它公开了QPoint类.我也包括PyQt4，它有一个饮酒者暴露的QPoint.我正在尝试完成两种类型之间的映射.

I used Boost.Python to create libui, which exposes the class QPoint. I aso included PyQt4, which has a sip-exposed QPoint. I'm trying to accomplish a mapping between the two types.

我检查了p是一个新样式的类，那么为什么__getattr__不被p.x()调用?

I checked that p is a new-style class, so why isn't __getattr__ being called for p.x()?

推荐答案

这与问题

This is somewhat similar to the issue someone else has encountered just yesterday. In short, it seems like special methods (like __getattr__, __str__, __repr__, __call__ and so on) aren't overridable in new-style class instance, i.e. you can only define them in its type.

这是我针对该问题的解决方案的改编版本，有望对您有用:

And here's an adaptation of my solution for that problem which should hopefully work for yours:

def _q_getattr(self, attr):
    print("get %s" % attr)
    return getattr(self, 'x')

def override(p, methods):
    oldType = type(p)
    newType = type(oldType.__name__ + "_Override", (oldType,), methods)
    p.__class__ = newType

override(p, { '__getattr__': _q_getattr})
print(p.__getattr__('x')())  # Works!  Prints "0"
print(p.x())                 # Should work!

这篇关于Python方法解析之谜的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！