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 Class.forName() 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

module = __import__("my_package/my_module")
the_class = getattr(module, "MyClass")
obj = the_class()

Answer 2

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

def my_import(name):
    mod = __import__(name)
    components = name.split('.')
    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', globals(), locals(), ['my_class'])
klass = getattr(mod, 'my_class')

Note that the last three arguments don't really do much other than provide context (so even though a list with 'my_class' in it was passed, my_class won't be imported into the local namespace).