traverse python print a directory and all files and directories inside

# Depth traversing print a folder 
DEF print_all_dir (dir): 
    # judge dir is the folder 
    IF os.path.isdir (dir): 
        # If it is a folder, the folder to print 
        Print (dir) 
        # re-iterate 
        for next_dir in os.listdir (dir): 
            # recursive call, clip continues to traverse the printing operation for each file in the folder / file, add the path to the file before 
            print_all_dir (os.path.join (dir, next_dir)) 
　　# judge dir is the file 
    elif os.path.isfile (dir): 
        # direct Print 
        Print (dir) 
　　# If neither a folder and not a file, the path does not exist, 
    the else: 
        # prompt and the end of the function 
        print ( "the path % s does not exist, please double-check! "dir%) 
        return 

in general, the path for a first operation to determine whether there is, but once inside the recursive call each will determine whether there is, the efficiency will be relatively low, so the judge put else only need to determine first-entered the path exists can be.