Why does “self” outside a function's parameters give a “not defined” error?

Question

Look at this code:

class MyClass():

    # Why does this give me \"NameError: name \'self\' is not defined\":
    mySelf = self

    # But this does not?
            


        

Answer 1

Note that self is not defined at the time when you want the class to refer to itself for the assignment to work. This is because (in addition to being named arbitrarily), self refers to instances and not classes. At the time that the suspect line of code attempts to run, there is as of yet no class for it to refer to. Not that it would refer to the class if there was.

In a method, you can always use type(self). That will get the subclass of MyClass that created the current instance. If you want to hard-code to MyClass, that name will be available in the global scope of the methods. This will allow you to do everything that your example would allow if it actually worked. E.g, you can just do MyClass.some_attribute inside your methods.

You probably want to modify the class attributes after class creation. This can be done with decorators or on an ad-hoc basis. Metaclasses may be a better fit. Without knowing what you actually want to do though, it's impossible to say.

UPDATE:

Here's some code to do what you want. It uses a metaclass AutoViewConfigMeta and a new decorator to mark the methods that you want view_config applied to. I spoofed the view_config decorator. It prints out the class name when it's called though to prove that it has access to it. The metaclass __new__ just loops through the class dictionary and looks for methods that were marked by the auto_view_config decorator. It cleans off the mark and applies the view_config decorator with the appropriate class name.

Here's the code.

# This just spoofs the view_config decorator.
def view_config(route=''):
    def dec(f):
        def wrapper(*args, **kwargs):
            print "route={0}".format(route)
            return f(*args, **kwargs)
        return wrapper
    return dec

# Apply this decorator to methods for which you want to call view_config with 
# the class name. It will tag them. The metaclass will apply view_config once it 
# has the class name. 
def auto_view_config(f):
    f.auto_view_config = True
    return f

class AutoViewConfigMeta(type):
    def __new__(mcls, name, bases, dict_):
        #This is called during class creation. _dict is the namespace of the class and
        # name is it's name. So the idea is to pull out the methods that need
        # view_config applied to them and manually apply them with the class name.
        # We'll recognize them because they will have the auto_view_config attribute
        # set on them by the `auto_view_config` decorator. Then use type to create
        # the class and return it.

        for item in dict_:
            if hasattr(dict_[item], 'auto_view_config'):  
                method = dict_[item]
                del method.auto_view_config # Clean up after ourselves.
                # The next line is the manual form of applying a decorator.
                dict_[item] = view_config(route=name)(method)  

        # Call out to type to actually create the class with the modified dict.
        return type.__new__(mcls, name, bases, dict_)


class simpleObject(object):
    __metaclass__ = AutoViewConfigMeta 


class Test(simpleObject):

    @auto_view_config
    def activateTheView(self):
        foo = 'bar'

        print foo

if __name__=='__main__':
    t = Test()
    t.activateTheView()

Let me know if you have any questions.