what about:

 def module_is_available(the_path,module_folder_name):    
    return module_folder_name in os.listdir(the_path)

or if you want to check all paths currently in sys.path:

def module_is_available_in_sys_path(module_folder_name):        
    for p in sys.path:
        if module_is_available(p,module_folder_name)
            return True
    return False