Converts MetricMetadata.ValueType enums to corresponding Python types.

def PythonTypeFromMetricValueType(value_type):
  """Converts MetricMetadata.ValueType enums to corresponding Python types."""
  if value_type == rdf_stats.MetricMetadata.ValueType.INT:
    return int
  elif value_type == rdf_stats.MetricMetadata.ValueType.FLOAT:
    return float
  else:
    raise ValueError("Unknown value type: %s" % value_type)