Return a resource finder for a package.
    :param package: The name of the package.
    :return: A :class:`ResourceFinder` instance for the package.

def finder(package):
    """
    Return a resource finder for a package.
    :param package: The name of the package.
    :return: A :class:`ResourceFinder` instance for the package.
    """
    if package in _finder_cache:
        result = _finder_cache[package]
    else:
        if package not in sys.modules:
            __import__(package)
        module = sys.modules[package]
        path = getattr(module, '__path__', None)
        if path is None:
            raise DistlibException('You cannot get a finder for a module, '
                                   'only for a package')
        loader = getattr(module, '__loader__', None)
        finder_maker = _finder_registry.get(type(loader))
        if finder_maker is None:
            raise DistlibException('Unable to locate finder for %r' % package)
        result = finder_maker(module)
        _finder_cache[package] = result
    return result