Function set_data_source 

pub(crate) fn set_data_source(source: Option<&Bound<'_, PyAny>>) -> PyResult<()>

Sets the process-wide default data source — any object with fetch(demand, as_of), and recipes(ask) where it serves recipes — or, with None, clears it. A market copies the default when it is built (MarketContext(...)); one built before this call keeps the source it had.