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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 build(self):
 """ Builds and returns all combinations of parameters specified by the param grid. """

        keys = self._param_grid.keys()
        grid_values = self._param_grid.values()

        def to_key_value_pairs(keys, values):
            return [(key, key.typeConverter(value)) for key, value in zip(keys, values)]

        return [dict(to_key_value_pairs(keys, prod)) for prod in itertools.product(*grid_values)]