Yield finders for the given module name
If fullname contains a '.', the finders will be for the package
containing fullname, otherwise they will be all registered top level
finders (i.e. those on both sys.meta_path and sys.path_hooks).
If the named module is in a package, that package is imported as a side
effect of invoking this function.
If no module name is specified, all top level finders are produced.