Erreur de tabulation?

File "liste_fichier.py", line 13
   taille += os.path.getsize(filename)
                                     ^
TabError: inconsistent use of tabs and spaces in indentation

# -*-coding:Latin-1 -*
import os, time

year = 365*24*60*60
source = "M:\\Expansion Immobilier\\Casino Developpement"
taille = 0

for root, direc, filenames in os.walk(source):
    for filename in filenames:
        if filename.lower().endswith(('.ppt', '.pptm', '.psd', '.dwg')):
            if time.time() - os.path.getatime(os.path.join(root, filename)) > 2*year:
                dir_path = os.path.join(root, filename)
                print(dir_path)
                taille += os.path.getsize(filename)
        if filename.lower().endswith(('.jpg', '.avi', '.ai', '.eps', '.bmp')):
            if time.time() - os.path.getatime(os.path.join(root, filename)) > 3*year:
                dir_path = os.path.join(root, filename)
                print(dir_path)
                taille += os.path.getsize(filename)
        if filename.lower().endswith(('.pst')):
            dir_path = os.path.join(root, filename)
            print(dir_path)
            taille += os.path.getsize(filename)

print("Les fichiers listé représente: ", taille)