parse lazy data with evaluated variables mapping.
            Notice: variables_mapping should not contain any variable or function.

def to_value(self, variables_mapping=None):
        """ parse lazy data with evaluated variables mapping.
            Notice: variables_mapping should not contain any variable or function.
        """
        variables_mapping = variables_mapping or {}

        args = []
        for arg in self._args:
            if isinstance(arg, LazyFunction):
                if self.cached and arg.cache_key and arg.cache_key in cached_functions_mapping:
                    value = cached_functions_mapping[arg.cache_key]
                else:
                    value = arg.to_value(variables_mapping)
                    cached_functions_mapping[arg.cache_key] = value
                args.append(value)
            else:
                # variable
                var_value = get_mapping_variable(arg, variables_mapping)
                args.append(var_value)

        if self._string == "{}":
            return args[0]
        else:
            return self._string.format(*args)