def user_directory_path(instance, filename):
 # file will be uploaded to MEDIA_ROOT/user_<id>/<filename>
 return 'user_{0}/{1}'.format(instance.user.id, filename)
class MyModel(models.Model):
 upload = models.FileField(upload_to=user_directory_path)

import hashlib
import os
import time
from django.utils.deconstruct import deconstructible
@deconstructible
class TimeStampFileName(object):
 def __init__(self, path):
  self.path = os.path.join(path, "%s%s")
 def __call__(self, instance, filename):
  extension = os.path.splitext(filename)[1]
  data = "%s_%d"%(filename,int(time.time()))
  file_hash = hashlib.sha1(data).hexdigest()
  return self.path % (file_hash, extension)

class MyModel(models.Model):
 upload = models.FileField(upload_to=TimeStampFileName('media/'), )