introspection

I regularly want to check if an object has a member or not. An example is the creation of a singleton in a function. For that purpose, you can use hasattr like this: class Foo(object): @classmethod def singleton(self): if not hasattr(self, 'instance'): self.instance = Foo() return self.instance But you can also do this: class Foo(object): @classmethod def singleton(self): try: return self.instance except AttributeError: self.instance = Foo() return self.instance Is one method better of the other? Edit: Added the @classmethod ... But note that the question is not about how to make a singleton

I am trying to figure out how to get the names of all decorators on a method. I can already get the method name and docstring, but cannot figure out how to get a list of decorators. If you can change the way you call the decorators from class Foo(object): @many @decorators @here def bar(self): pass to class Foo(object): @register(many,decos,here) def bar(self): pass then you could register the decorators this way: def register(*decorators): def register_wrapper(func): for deco in decorators[::-1]: func=deco(func) func._decorators=decorators return func return register_wrapper For example: def

What's the shortest, one-liner way to list all methods defined with attr_accessor ? I would like to make it so, if I have a class MyBaseClass , anything that extends that, I can get the attr_accessor 's defined in the subclasses. Something like this: class MyBaseClass < Hash def attributes # ?? end end class SubClass < MyBaseClass attr_accessor :id, :title, :body end puts SubClass.new.attributes.inspect #=> [id, title, body] What about to display just the attr_reader and attr_writer definitions? There is no way (one-liner or otherwise) to list all methods defined by attr_accessor and only

This is primarily a curiosity, I'm not really sure what's the practical use of this but here goes. Since blocks are also Objective-C objects, is it possible to check their type? That is, does it respond to the isKindOfClass: message and how to use that message with respect to blocks? My naive thought that it's probably like this: -(void) aMethod { typedef int (^BlockA)(int x, int y); id blockVar = ...; // get a block from somewhere if([blockVar isKindOfClass:BlockA]) { BlockA blockVarA = blockVar; int result = blockVarA(1,2); } } The code above probably won't work. But if it is possible to

I've already seen the following question but it doesn't quite get me where I want: How can I get a list of all classes within current module in Python? In particular, I do not want classes that are imported, e.g. if I had the following module: from my.namespace import MyBaseClass from somewhere.else import SomeOtherClass class NewClass(MyBaseClass): pass class AnotherClass(MyBaseClass): pass class YetAnotherClass(MyBaseClass): pass If I use clsmembers = inspect.getmembers(sys.modules[__name__], inspect.isclass) like the accepted answer in the linked question suggests, it would return

Say you have a javascript object like this: var data = { foo: 'bar', baz: 'quux' }; You can access the properties by the property name: var foo = data.foo; var baz = data["baz"]; But is it possible to get these values if you don't know the name of the properties? Does the unordered nature of these properties make it impossible to tell them apart? In my case I'm thinking specifically of a situation where a function needs to accept a series of name-value pairs, but the names of the properties may change. My thoughts on how to do this so far is to pass the names of the properties to the function