code: def is_uid(uid, validate=False):
      
      if not isinstance(uid, basestring):
          return False
      if uid == '0':
          return True
      if len(uid) != 32:
          return False
      if not UID_RX.match(uid):
          return False
      if not validate:
          return True
  
      # Check if a brain for this uid exists
      uc = get_tool('uid_catalog')
      brains = uc(UID=uid)
      if brains:
          assert (len(brains) == 1)
      return len(brains) > 0
docs: Checks if the passed in uid is a valid UID
  
      :param uid: The uid to check
      :param validate: If False, checks if uid is a valid 23 alphanumeric uid. If
      True, also verifies if a brain exists for the uid passed in
      :type uid: string
      :return: True if a valid uid
      :rtype: bool