Here is a pretty good explanation of the matter by Greg Parker Quoting: […] Each Objective-C class is also an object. It has an isa pointer and other data, and can respond to selectors. When you call a “class method” like [NSObject alloc], you are actually sending a message to that class object. Since a … Read more
In the current version of Python, the class ordering is preserved. See PEP520 for details. In older versions of the language (3.5 and below, but not 2.x), you can provide a metaclass which uses an OrderedDict for the class namespace. import collections class OrderedClassMembers(type): @classmethod def __prepare__(self, name, bases): return collections.OrderedDict() def __new__(self, name, bases, … Read more
An elegant way to do it is described in Michael Foord’s Voidspace blog in an entry about what metaclasses are and how to use them in the section titled A Method Decorating Metaclass. Simplifying it slightly and applying it to your situation resulted in this: from functools import wraps from types import FunctionType def wrapper(method): … Read more
The best (and only) cases I have seen so far for subclassing EnumMeta comes from these four questions: A more pythonic way to define an enum with dynamic members Prevent invalid enum attribute assignment Create an abstract Enum class Invoke a function when an enum member is accessed We’ll examine the dynamic member case further … Read more
how do this work Easy: it doesn’t. Not in Ruby, anyway. Just like in most other languages, there are some core entities that are simply assumed to exist. They fall from the sky, materialize out of thin air, magically appear. In Ruby, some of those magic things are: Object doesn’t have a superclass, but you … Read more
First, the class << foo syntax opens up foo‘s singleton class (eigenclass). This allows you to specialise the behaviour of methods called on that specific object. a=”foo” class << a def inspect ‘”bar”‘ end end a.inspect # => “bar” a=”foo” # new object, new singleton class a.inspect # => “foo” Now, to answer the question: … Read more
Creating a singleton in Python
Classes as objects Before understanding metaclasses, you need to master classes in Python. And Python has a very peculiar idea of what classes are, borrowed from the Smalltalk language. In most languages, classes are just pieces of code that describe how to produce an object. That’s kinda true in Python too: >>> class ObjectCreator(object): … … Read more