子类化ctypes-Python
问题说明
这是我在互联网上找到的一些代码。我不确定该如何使用。我只是用枚举键/值填充了 members ,并且它起作用了,但是我很好奇这个元类的全部含义。我假设它与ctypes有关,但是我找不到关于ctypes子类化的很多信息。我知道EnumerationType并没有使用我使用Enumeration的方式。
This is some code I found on the internet. I'm not sure how it is meant to be used. I simply filled members with the enum keys/values and it works, but I'm curious what this metaclass is all about. I am assuming it has something to do with ctypes, but I can't find much information on subclassing ctypes. I know EnumerationType isn't doing anything the way I'm using Enumeration.
from ctypes import *
class EnumerationType(type(c_uint)):
def __new__(metacls, name, bases, dict):
if not "_members_" in dict:
_members_ = {}
for key,value in dict.items():
if not key.startswith("_"):
_members_[key] = value
dict["_members_"] = _members_
cls = type(c_uint).__new__(metacls, name, bases, dict)
for key,value in cls._members_.items():
globals()[key] = value
return cls
def __contains__(self, value):
return value in self._members_.values()
def __repr__(self):
return "<Enumeration %s>" % self.__name__
class Enumeration(c_uint):
__metaclass__ = EnumerationType
_members_ = {}
def __init__(self, value):
for k,v in self._members_.items():
if v == value:
self.name = k
break
else:
raise ValueError("No enumeration member with value %r" % value)
c_uint.__init__(self, value)
@classmethod
def from_param(cls, param):
if isinstance(param, Enumeration):
if param.__class__ != cls:
raise ValueError("Cannot mix enumeration members")
else:
return param
else:
return cls(param)
def __repr__(self):
return "<member %s=%d of %r>" % (self.name, self.value, self.__class__)
And an enumeration probably done the wrong way.
class TOKEN(Enumeration):
_members_ = {'T_UNDEF':0, 'T_NAME':1, 'T_NUMBER':2, 'T_STRING':3, 'T_OPERATOR':4, 'T_VARIABLE':5, 'T_FUNCTION':6}
正确答案
元类是用于创建类的类。这样想:所有对象都有一个类,一个类也是一个对象,因此,一个类可以具有一个类是有意义的。
A metaclass is a class used to create classes. Think of it this way: all objects have a class, a class is also an object, therefore, it makes sense that a class can have a class.
http://www.ibm.com/developerworks/linux/library/l-pymeta .html
要了解其作用,您可以查看代码中的几点。
To understand what this is doing, you can look at a few points in the code.
_members_ = {'T_UNDEF':0, 'T_NAME':1, 'T_NUMBER':2, 'T_STRING':3, 'T_OPERATOR':4, 'T_VARIABLE':5, 'T_FUNCTION':6}
globals()[key] = value
这里需要使用字典中定义的每个键: T_UNDEF和 T_NUMBER,并使其在您的全局字典中可用。
Here it takes every defined key in your dictionary: "T_UNDEF" "T_NUMBER" and makes them available in your globals dictionary.
def __init__(self, value):
for k,v in self._members_.items():
if v == value:
self.name = k
break
无论何时创建枚举实例,它将在初始化类时检查值是否在允许的枚举名称列表中。找到值时,它将字符串名称设置为self.name。
Whenever you make an instance of your enum, it will check to see if the "value" is in your list of allowable enum names when you initialized the class. When the value is found, it sets the string name to self.name.
c_uint.__init__(self, value)
这是将 ctypes值设置为实际的c无符号整数的实际行。
This is the actual line which sets the "ctypes value" to an actual c unsigned integer.
这篇好文章是转载于:学新通技术网
- 版权申明: 本站部分内容来自互联网,仅供学习及演示用,请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系,请提供相关证据及您的身份证明,我们将在收到邮件后48小时内删除。
- 本站站名: 学新通技术网
- 本文地址: /reply/detail/tanhcfkjjh
-
YouTube API 不能在 iOS (iPhone/iPad) 工作,但在桌面浏览器工作正常?
it1352 07-30 -
iPhone,一张图像叠加到另一张图像上以创建要保存的新图像?(水印)
it1352 07-17 -
保持在后台运行的 iPhone 应用程序完全可操作
it1352 07-25 -
使用 iPhone 进行移动设备管理
it1352 07-23 -
在android同时打开手电筒和前置摄像头
it1352 09-28 -
扫描 NFC 标签时是否可以启动应用程序?
it1352 08-02 -
检查邮件是否发送成功
it1352 07-25 -
Android微调工具-删除当前选择
it1352 06-20 -
希伯来语的空格句子标记化错误
it1352 06-22 -
Android App 和三星 Galaxy S4 不兼容
it1352 07-20