浓缩pyqtproperties

Question

我正在用Python编写脚本，但有一个问题：

class LightDMUser(QObject):
  def __init__(self, user):
    super(LightDMUser, self).__init__()
    self.user = user

  @pyqtProperty(QVariant)
  def background(self):      return self.user.get_background()

  @pyqtProperty(QVariant)
  def display_name(self):    return self.user.get_display_name()

  @pyqtProperty(QVariant)
  def has_messages(self):    return self.user.get_has_messages()

  @pyqtProperty(QVariant)
  def home_directory(self):  return self.user.get_home_directory()

  @pyqtProperty(QVariant)
  def image(self):           return self.user.get_image()

  @pyqtProperty(QVariant)
  def language(self):        return self.user.get_language()

  @pyqtProperty(QVariant)
  def layout(self):          return self.user.get_layout()

  @pyqtProperty(QVariant)
  def layouts(self):         return self.user.get_layouts()

  @pyqtProperty(QVariant)
  def logged_in(self):       return self.user.get_logged_in()

  @pyqtProperty(QVariant)
  def name(self):            return self.user.get_name()

  @pyqtProperty(QVariant)
  def real_name(self):       return self.user.get_real_name()

  @pyqtProperty(QVariant)
  def session(self):         return self.user.get_session()

如您所见，此代码非常多余。我试着像这样压缩它：

class LightDMUser(QObject):
  attributes = ['background', 'display_name', 'has_messages', 'home_directory', 'image', 'language', 'layout', 'layouts', 'logged_in', 'name', 'real_name', 'session']

  def __init__(self, user):
    super(LightDMUser, self).__init__()
    self.user = user

    for attribute in self.attributes:
      setattr(self, attribute, pyqtProperty(QVariant, getattr(self.user, 'get_' + attribute)))

但是，PyQt4期望为类本身而不是实例提供类方法。因为没有为该类定义setattr代码，所以将代码移出该__init__块也不起作用self，所以我真的不知道该怎么做。

谁能看到压缩此代码的方法？

Answer 1

有很多方法可以做到：类装饰器，元类和Mixin。

常用助手功能：

def set_pyqtproperties(klass, properties, proxy='user'):
    def make_prop(prop):        
        def property_(self):
            return getattr(getattr(self, proxy), 'get_' + prop)
        property_.__name__ = prop
        return property_

    if isinstance(properties, basestring):
       properties = properties.split()
    for prop in properties:
         setattr(klass, prop, pyqtProperty(QVariant, make_prop(prop)))

类装饰器

def set_properties(properties):
    def decorator(klass):
        set_pyqtproperties(klass, properties)
        return klass
    return decorator

用法

@set_properties("display background")
class LightDMUser(QObject): pass

如果不支持类装饰器，则可以尝试：

class LightDMUser(QObject): 
    pass
LightDMUser = set_properties("display background")(LightDMUser)

元类

def set_properties_meta(properties):
    def meta(name, bases, attrs):
        cls = type(name, bases, attrs)
        set_pyqtproperties(cls, properties)
        return cls
    return meta

用法

class LightDMUser(QObject):
    __metaclass__ =  set_properties_meta("display background")

注意：如果将属性列表设置为类属性，则可以重用同一元类：

def MetaClass(name, bases, attrs):
    cls = type(name, bases, attrs)
    set_pyqtproperties(cls, attrs.get('properties', ''))
    return cls

class LightDMUser(QObject):
    properties = "display background"
    __metaclass__ = MetaClass

另外，您可以attrs直接attrs[name] = value进行操作：在调用之前type()代替setattr(cls, name, value)。

以上假设QObject.__class__ is type。

混合蛋白

def properties_mixin(classname, properties):
    #note: create a new class by whatever means necessary
    # e.g., even using exec() as namedtuple does
    # http://hg.python.org/cpython/file/3.2/Lib/collections.py#l235

    # reuse class decorator here
    return set_properties(properties)(type(classname, (), {}))

用法

PropertiesMixin = properties_mixin('PropertiesMixin', 'display background')
class LightDMUser(PropertiesMixin, QObject): pass

我还没有尝试过。这里的代码显示了实现该功能可能需要的数量和代码种类。