How do I add an instance method to a class using a metaclass (yes I do need to use a metaclass)? The following kind of works, but the func_name will still be "foo": def bar(self): print "bar" class MetaFoo(type): __new__(cls, name, bases, dict): dict["foobar"] = bar return type(name, bases, dict) class Foo(obje...
The problem: I have a class which contains a template method "execute" which calls another method "_execute". Subclasses are supposed to overwrite "_execute" to implement some specific functionality. This functionality should naturally be documented in the docstring of "_execute". I also expect users to create their own subclasses to ex...
I´ve mastered almost all the Python concepts (well, let´s say there are just OO concepts :-)) but this one is tricky. I know it has something to do with introspection but it´s still unclear to me. So what are metaclasses? What do you use them for? Concrete examples, including snippets, much appreciated! ...
In the context of a Google App Engine Webapp framework application: I want to changed the request verb of a request in the case a parameter _method is provided, for example if a POST request comes in with a parameter _method=PUT, I need to change the request to call the put method of the handler. This is to cope with the way prototype.j...
I have a friend who likes to use metaclasses, and regularly offers them as a solution. I am of the mind that you almost never need to use metaclasses. Why? because I figure if you are doing something like that to a class, you should probably be doing it to an object. And a small redesign/refactor is in order. Being able to use metaclas...
I have read posts like these: What is a metaclass in Python? What are your (concrete) use-cases for metaclasses in Python? Python's Super is nifty, but you can't use it but somehow I got confused, many confusions like when and why i would have to do something like this #refer link1 return super(MyType, cls).__new__(cls, name, bas...
I recently discovered metaclasses in python. Basically a metaclass in python is a class that creates a class. There are many useful reasons why you would want to do this - any kind of class initialisation for example. Registering classes on factories, complex validation of attributes, altering how inheritance works, etc. All of this be...
Using Groovy's package name convention, I can intercept Groovy method calls to a Java method like so: package groovy.runtime.metaclass.org.myGang.myPackage class FooMetaClass extends groovy.lang.DelegatingMetaClass { StringMetaClass(MetaClass delegate) { super(delegate); } public Object getProperty(Object a, St...
This is a contrived example of what I want to do, but minimally expresses the behavior desired. I want to reference the instance of the object on which the property access is being invoked. I tried 'this' first, but that refers to the enclosing class rather than either the MetaClass or the String instance. String.metaClass.propertyMi...
Hi, guys! I'm in a big trouble with uml profile implementation. The problem is I can't get how can I extend uml Operation class from Infrastructure::Core::Constructs using Profile? The Extension association from Profiles package allow metaclass only to be of type Core::Constructs::Class according to uml metamodel. Is Operation a met...
I've been hacking classes in python like this : def hack(f,aClass) : class MyClass(aClass) : def f(self) : f() return MyClass A = hack(afunc,A) Which looks pretty clean to me. It takes a class A, creates a new class derived from it, that has an extra method, calling f, and then reassigns the new clas to A. How does t...
I've been reading a bit about what metaclasses are, but I would like to know if they can be achieved in C++. I know that Qt library is using MetaObjects, but it uses an extension of C++ to achieve it. I want to know if it is possible directly in C++. Thanks. ...
Let's say we've got a metaclass CallableWrappingMeta which walks the body of a new class, wrapping its methods with a class, InstanceMethodWrapper: import types class CallableWrappingMeta(type): def __new__(mcls, name, bases, cls_dict): for k, v in cls_dict.iteritems(): if isinstance(v, types.FunctionType): ...
I've been trying to learn about metaclasses in Python. I get the main idea, but I can't seem to activate the mechanism. As I understand it, you can specify M to be as the metaclass when constructing a class K by setting __metaclass__ to M at the global or class level. To test this out, I wrote the following program: p = print class M(t...
I'm relatively new to Groovy and Grails and am trying them out in my spare time. I've got a small test Grails application that I'm able to run fine using grails run-app, but grails run-war results in an error. In the grails-app/conf/BootStrip.init method, I'm adding some property getters onto the DefaultGrailsControllerClass and Defaul...
Hi all, I have some code in Python where I'll have a bunch of classes, each of which will have an attribute _internal_attribute. I would like to be able to generate a mapping of those attributes to the original class. Essentially I would like to be able to do this: class A(object): _internal_attribute = 'A attribute' class B(object...
See the code below. Old instances of a class created before a method is added to the class using metaClass should not understand the method right? The assert statement below the 'PROBLEMATIC LINE' comment is executed when I think it should not be, as the old parentDir instance should not understand the blech() message. // derived from...
From Snipplr Ok here is the script code, in the comments is the question and the exception thrown class Class1 { def closure = { println this.class.name println delegate.class.name def nestedClos = { println owner.class.name } nestedClos() } } def clos = new Class1().closure ...
I'm having trouble to understand how a classmethod object works in Python, especially in the context of metaclasses and in __new__. In my special case I would like to get the name of a classmethod member, when I iterate through the members that were given to __new__. For normal methods the name is simply stored in a __name__ attribute, ...
EDIT: this post only applies to Ruby 1.9 Hi, At the toplevel method definition should result in private methods on Object, and tests seem to bear this out: def hello; "hello world"; end Object.private_instance_methods.include?(:hello) #=> true Object.new.send(:hello) #=> "hello world" However, the following also works (at toplevel)...