How to dynamically load a Python class

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()

From stackoverflow

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

  Jason Baker : Note that this works because of a bug in the __import__ function. File paths should *not* be used in the __import__ function and will not work in python 2.6 and above: http://docs.python.org/whatsnew/2.6.html#porting-to-python-2-6

• 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).

  pjesi : I tried my_import('my_package.my_module.my_class') but get no module found my_class, which makes sense since it is a class not a module. Howver if I can use gettattr to get the class after the call to my_import

  Jason Baker : That's odd. Everything past the first dot is called using getattr. There shouldn't be any difference.

  Jason Baker : Figured it out. See the post edit.

  pjesi : Thanks I think this is the best way. Now I only need the best way to split the string 'my_pakcage.my_module.my_class' into mod_name, klass_name but I guess I can figure that out :)