def _function_lookup(name, module):
    """Searches the function between the registered ones.
    If not found, it imports the module forcing its registration.

    """
    try:
        return _registered_functions[name]
    except KeyError:  # force function registering
        __import__(module)
        mod = sys.modules[module]
        getattr(mod, name)

        return _registered_functions[name]
Searches the function between the registered ones.
    If not found, it imports the module forcing its registration.