ValueError: chr() arg not in range(256)

[abitofalchemy]

@tweninger the error I get when I try to derive rules from a .dimacs.tree file, which is generated using INDDGO:

chr() arg not in range(256)
Traceback (most recent call last):
File "tredec.phrg.py", line 163, in
main()
File "tredec.phrg.py", line 158, in main
dimacs_td_ct(args['clqtree'], args['orig']) # gen synth graph
File "tredec.phrg.py", line 106, in dimacs_td_ct
td.new_visit(T, G, prod_rules)
File "/home/saguinag/Research/TreeDecomps/tdec/tree_decomposition.py", line 211, in new_visit
new_visit(subtree, G, prod_rules, indent=indent+2, parent=node)
File "/home/saguinag/Research/TreeDecomps/tdec/tree_decomposition.py", line 206, in new_visit
add_to_prod_rules(prod_rules, itx, rhs, s)
File "/home/saguinag/Research/TreeDecomps/tdec/tree_decomposition.py", line 244, in add_to_prod_rules
letter=chr(ord(letter) + 1)
ValueError: chr() arg not in range(256)

Recreate the error:
python tredec.phrg.py --orig /data/saguinag/datasets/time_stamped_datasets/out.CollegeMsg --clqtree datasets/CollegeMsg_mcs.dimacs.tree