Sets an attribute of the symbol.

        For example. A._set_attr(foo="bar") adds the mapping ``"{foo: bar}"``
        to the symbol's attribute dictionary.

        Parameters
        ----------
        **kwargs
            The attributes to set

def _set_attr(self, **kwargs):
        """Sets an attribute of the symbol.

        For example. A._set_attr(foo="bar") adds the mapping ``"{foo: bar}"``
        to the symbol's attribute dictionary.

        Parameters
        ----------
        **kwargs
            The attributes to set
        """
        for key, value in kwargs.items():
            if not isinstance(value, string_types):
                raise ValueError("Set Attr only accepts string values")
            check_call(_LIB.MXSymbolSetAttr(
                self.handle, c_str(key), c_str(str(value))))