python 3 filter()

gistfile1.txt

def sanitize_username(self, s):
  """Takes a string and returns it with only allowed characters."""
  # http://stackoverflow.com/questions/12756156/with-python-what-is-the-most-efficient-way-to-remove-all-char-from-string-excep#comment17236154_12756156
  # a-z, A-Z, 0-9, _, -, .
  keep_set = set(string.ascii_letters + string.digits + '_-.')
  return filter(keep_set.__contains__, s)
  
sanitize_username('chrickso') returns <filter object at 0x10c53aa58>


def sanitize_username(self, s):
  """Takes a string and returns it with only allowed characters."""
  # http://stackoverflow.com/questions/12756156/with-python-what-is-the-most-efficient-way-to-remove-all-char-from-string-excep#comment17236154_12756156
  # a-z, A-Z, 0-9, _, -, .
  keep_set = set(string.ascii_letters + string.digits + '_-.')
  return list(filter(keep_set.__contains__, s))

sanitize_username('chrickso') returns ['c', 'h', 'r', 'i', 'c', 'k', 's', 'o']


how can i get it to return 'chrickso' ?