file-rename-use-date.py

import os
import datetime
import glob

def modification_date(filename):
    t = os.path.getmtime(filename)
    return datetime.datetime.fromtimestamp(t)

files = glob.glob('*')

for l in files:
    if l.endswith('py'):
        continue
    dt = modification_date(l)
    out = dt.strftime("%Y%m%d")
    newname = '%s-%s' % ( out,l,)
    print newname
    os.rename(l, newname)