This recursive function written in python3 returns the total size of a directory.

recursive_dir_size

import os

def recursive_dir_size(path):
    size = 0
    
    for x in os.listdir(path):
        if not os.path.isdir(os.path.join(path,x)):
            size += os.stat(os.path.join(path,x)).st_size
        else:
            size += recursive_dir_size(os.path.join(path,x))
    
    return size