Function pio_parse_file 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_parse_file(
    path: *const c_char,
    from: *const c_char,
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut PioNetwork

Parse path (format from extension, or from if non-NULL) into a case handle. from accepts the pio_parse_str format names plus pypsa-csv/pypsa; a PyPSA CSV folder is a directory, so it can only enter through this function, with from = "pypsa-csv" (or NULL when the directory holds a network.csv). Read fidelity warnings attach to the handle (pio_parse_warnings). Returns NULL on error and writes the message into errbuf.