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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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))))