def write(out_fn, fn_idx):
xc = XigtCorpus()
for fn, igt_indices in fn_idx.items():
# if possible, try to decode needed igts only and skip the rest
in_xc = xigtxml.load(fn, mode='transient')
# ignoring corpus-level metadata
xc.extend(igt for i, igt in enumerate(in_xc) if i in igt_indices)
# assume the nsmap of the first igt is the same for all
if xc.igts: xc.nsmap = xc[0].nsmap
xigtxml.dump(out_fn, xc)
