reflection - How to dynamically load a Python class

Question

Given a string of a Python class, e.g. my_package.my_module.MyClass, what is the best possible way to load it?

In other words I am looking for a equivalent Class.forName() in Java, function in Python. It needs to work on Google App Engine.

Preferably this would be a function that accepts the FQN of the class as a string, and returns a reference to the class:

my_class = load_class('my_package.my_module.MyClass')
my_instance = my_class()

Answer 1

From the python documentation, here's the function you want:

def my_import(name):
    components = name.split('.')
    mod = __import__(components[0])
    for comp in components[1:]:
        mod = getattr(mod, comp)
    return mod

The reason a simple __import__ won't work is because any import of anything past the first dot in a package string is an attribute of the module you're importing. Thus, something like this won't work:

__import__('foo.bar.baz.qux')

You'd have to call the above function like so:

my_import('foo.bar.baz.qux')

Or in the case of your example:

klass = my_import('my_package.my_module.my_class')
some_object = klass()

EDIT: I was a bit off on this. What you're basically wanting to do is this:

from my_package.my_module import my_class

The above function is only necessary if you have a empty fromlist. Thus, the appropriate call would be like this:

mod = __import__('my_package.my_module', fromlist=['my_class'])
klass = getattr(mod, 'my_class')