code: def locked_get(self):
          
          credentials = None
          _helpers.validate_file(self._filename)
          try:
              f = open(self._filename, 'rb')
              content = f.read()
              f.close()
          except IOError:
              return credentials
  
          try:
              credentials = client.Credentials.new_from_json(content)
              credentials.set_store(self)
          except ValueError:
              pass
  
          return credentials
docs: Retrieve Credential from file.
  
          Returns:
              oauth2client.client.Credentials
  
          Raises:
              IOError if the file is a symbolic link.