parameters: (self, option, default=None)
docstring: Ensure that 'option' is a string; if not defined, set it to
          'default'.
docstring_summary: Ensure that 'option' is a string; if not defined, set it to
          'default'.
docstring_tokens: Ensure that option is a string ; if not defined set it to default .
function: def ensure_string (self, option, default=None):
          """Ensure that 'option' is a string; if not defined, set it to
          'default'.
          """
          self._ensure_stringlike(option, "string", default)
function_tokens: def ensure_string ( self , option , default = None ) : self . _ensure_stringlike ( option , "string" , default )