metaclass

PyQt5: Issues with a Mixin with a metaclass within a derived QWidget class

由 扶醉桌前 提交于 2019-12-08 03:36:53
问题 I'm having issues trying to add a mixin with a metaclass to a class whose base is a QWidget. I'm aware that PyQt5 supports cooperative multiple inheritance and if my MixIn class has no metaclass then things work fine. However, if it has a metaclass - whether it be the pyqtWrapperType metaclass shared by QWidgets or a derived metaclass, then I receive the following error: Process finished with exit code -1073741819 (0xC0000005) The code for the rest of the script runs, but the QWidget does not

In Python, decorate two methods with the same name to distinguish them

由 心已入冬 提交于 2019-12-08 01:36:35
问题 I am writing a framework to be used by people who know some python. I have settled on some syntax, and it makes sense to me and them to use something like this, where Base is the Base class that implements the framework. class A(Base): @decorator1 @decorator2 @decorator3 def f(self): pass @decorator4 def f(self): pass @decorator5 def g(self) pass All my framework is implemented via Base's metaclass. This set up is appropriate for my use case because all these user-defined classes have a rich

how does metaclass work with the MRO list when super() is called?

由 家住魔仙堡 提交于 2019-12-07 18:34:06
问题 I'm really confused by the following code sample: class Meta_1(type): def __call__(cls, *a, **kw): # line 1 print("entering Meta_1.__call__()") print(cls) # line 4 print(cls.mro()) # line 5 print(super(Meta_1, cls).__self__) # line 6 rv = super(Meta_1, cls).__call__(*a, **kw) # line 7 print("exiting Meta_1.__call__()") return rv class Car(object, metaclass=Meta_1): def __new__(cls, *a, **kw): print("Car.__new__()") rv = super(Car, cls).__new__(cls, *a, **kw) return rv def __init__(self, *a, *

The built-in keyword type means a function or a class in python?

由 半腔热情 提交于 2019-12-07 14:32:46
问题 In most posts, people often say type is a built-in function if it is provided with one argument, and it is a metaclass if provided with 3 arguments. But in python's doc, the signature of type is: class type(object) class type(name, bases, dict) So, does it means type is a built-in class and not a built-in function even if it is provided with one argument? 回答1: type is called a "metaclass" because it's a class that produces other classes (AKA types). It behaves like a normal class. In

how do i subclass threading.Event?

由 北慕城南 提交于 2019-12-07 12:25:46
问题 In Python 2.7.5: from threading import Event class State(Event): def __init__(self, name): super(Event, self).__init__() self.name = name def __repr__(self): return self.name + ' / ' + self.is_set() I get: TypeError: Error when calling the metaclass bases function() argument 1 must be code, not str Why? Everything I know about threading.Event I learned from: http://docs.python.org/2/library/threading.html?highlight=threading#event-objects What does it mean when it says that threading.Event()

Setting metaclass of wrapped class with Boost.Python

由 回眸只為那壹抹淺笑 提交于 2019-12-07 04:44:18
问题 I have an Event class defined in C++ that I expose to Python using Boost. My scripts are expected to derive from this class, and I'd like to do some initialization whenever a new child class is defined. How can I set the metaclass of the exposed Event class such that whenever a Python script derives from this class, the metaclass could do the required initialization? I would like to avoid having to explicitly use a metaclass in the scripts... class KeyboardEvent(Event): # This is what I want

How to convert a string with the name of a class to the class type itself?

由 ╄→гoц情女王★ 提交于 2019-12-06 23:17:19
问题 In order to store a class name in a log file I converted the description of a class type to a string: let objectType: NSObject.Type = Object.self let str = String(describing: objectType) However, I do not succeed in back conversion of str to a variable of type NSObject.Type to use it in a generic method. How could I do this? 回答1: You can get your class back from string , but you need to use your project's module name while getting class name. If you don't use your module name then it will

深刻理解Python中的元类(metaclass)

由 倾然丶 夕夏残阳落幕 提交于 2019-12-06 15:50:43
深刻理解Python中的元类(metaclass) 译注： 这是一篇在 Stack overflow 上很热的帖子。提问者自称已经掌握了有关Python OOP编程中的各种概念，但始终觉得元类(metaclass)难以理解。他知道这肯定和自省有关，但仍然觉得不太明白，希望大家可以给出一些实际的例子和代码片段以帮助理解，以及在什么情况下需要进行元编程。于是e-satis同学给出了神一般的回复，该回复获得了985点的赞同点数，更有人评论说这段回复应该加入到Python的官方文档中去。而e-satis同学本人在Stack Overflow中的声望积分也高达64271分。以下就是这篇精彩的回复（提示：非常长） 类也是对象 在理解元类之前，你需要先掌握Python中的类。Python中类的概念借鉴于Smalltalk，这显得有些奇特。在大多数 编程语言 中，类就是一组用来描述如何生成一个对象的代码段。在Python中这一点仍然成立： 1 2 3 4 5 6 >>>classObjectCreator(object): … pass … >>> my_object=ObjectCreator() >>>printmy_object <__main__.ObjectCreatorobjectat0x8974f2c> 但是，Python中的类还远不止如此。类同样也是一种对象。是的，没错，就是对象

how does metaclass work with the MRO list when super() is called?

由 孤街浪徒 提交于 2019-12-06 14:28:43
I'm really confused by the following code sample: class Meta_1(type): def __call__(cls, *a, **kw): # line 1 print("entering Meta_1.__call__()") print(cls) # line 4 print(cls.mro()) # line 5 print(super(Meta_1, cls).__self__) # line 6 rv = super(Meta_1, cls).__call__(*a, **kw) # line 7 print("exiting Meta_1.__call__()") return rv class Car(object, metaclass=Meta_1): def __new__(cls, *a, **kw): print("Car.__new__()") rv = super(Car, cls).__new__(cls, *a, **kw) return rv def __init__(self, *a, **kw): print("Car.__init__()") super(Car,self).__init__(*a, **kw) if __name__ == '__main__': c = Car()

In Objective C, how to obtain the metaclass object?

由 我怕爱的太早我们不能终老 提交于 2019-12-06 11:36:25
In Objective-C , how does one obtain the metaclass object? Both [self class] and [ClassName class] returns the Class object only. objc_getMetaClass Edit: Improved as per Greg's suggestion in the comments. object_getClass([Class class]); object_getClass([self class]) object_getClass([ClassName class]) You'll probably have to use the objective-C runtime function object_getClass to get the class of the class object. A good write up What is a meta-class in Objective-C goes through some detail on meta-classes. However, in some cases the class of the meta-class is the class itself. Do you wish to
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