PYTHON - Wait for completion of a copy of files before executing the next steps

Question

Hello I am creating a backup routine that consists of copying a series of files from one folder to another. After copying the file I want to run a getsize to recover the size of the directory. The problem is that getsize runs before the copy is finished. How do I have each step run only at the end of the previous?

import os
from datetime import date

today = str(date.today()).replace("-","")
todayformated = date.today().strftime("%d/%m/%Y")
source = "D:\\Origem\\"
destination = "D:\\Destino\\"
sourcebkpini = "D:\\backup.ini"
backupini = """[BACKUP]
DataBackup="""+todayformated+"""
DirDestinoBackup=
"""

def execBackup():
    try:
        os.popen('mkdir '+ destination+today)
        os.popen('copy ' + source + '* ' + destination+today, 'w')
        with open(sourcebkpini, 'w') as ini:
            ini.write(backupini)
            print('Calculando tamanho do diretório', os.path.getsize(destination+today))
    except:
        print("Erro")

execBackup()


retorno:

Calculando tamanho do diretório 4096
D:\Origem\imovel.DB
D:\Origem\imovel.MB
D:\Origem\imovel.PX
D:\Origem\imovel.XG0