def decode_lattice(lattice: pynini.Fst, lm: pynini.Fst,
sym: pynini.SymbolTable) -> str:
"""Decodes the lattice."""
lattice = pynini.compose(lattice, lm)
assert lattice.start() != pynini.NO_STATE_ID, "composition failure"
# Pynini can join the string for us.
return pynini.shortestpath(lattice).rmepsilon().string(sym)
def all_suffixes(self, fsa: pynini.Fst) -> pynini.Fst:
fsa = fsa.copy()
start_state = fsa.start()
for s in fsa.states():
fsa.add_arc(
start_state,
pynini.Arc(0, 0, pynini.Weight.one(fsa.weight_type()), s))
return fsa.optimize()
def compile_wfst_from_right_branching_grammar(grammar):
"""
:type grammar: LCFRS
:rtype: Fst
Create a FST from a right-branching hybrid grammar.
The Output of the is a rule tree in `polish notation <https://en.wikipedia.org/wiki/Polish_notation>`_
"""
myfst = Fst()
nonterminals = SymbolTable()
for nont in grammar.nonts():
sid = myfst.add_state()
nonterminals.add_symbol(nont, sid)
if nont == grammar.start():
myfst.set_start(sid)
sid = myfst.add_state()
nonterminals.add_symbol(FINAL, sid)
myfst.set_final(nonterminals.add_symbol(FINAL))
rules = Enumerator(first_index=1)
for rule in grammar.rules():
rules.object_index(rule)
terminals = SymbolTable()
terminals.add_symbol('<epsilon>', 0)
for rule in grammar.rules():
if len(rule.rhs()) == 2:
for rule2 in grammar.lhs_nont_to_rules(rule.rhs_nont(0)):
if len(rule2.rhs()) == 0:
arc = Arc(terminals.add_symbol(rule2.lhs().args()[0][0]),
terminals.add_symbol(str(rules.object_index(rule))
+ '-' + str(rules.object_index(rule2))),
make_weight(rule.weight() * rule2.weight()),
nonterminals.find(rule.rhs_nont(1)))
myfst.add_arc(nonterminals.find(rule.lhs().nont()), arc)
elif len(rule.rhs()) == 0:
arc = Arc(terminals.add_symbol(rule.lhs().args()[0][0]),
terminals.add_symbol(str(rules.object_index(rule))), make_weight(rule.weight()),
nonterminals.find(FINAL))
myfst.add_arc(nonterminals.find(rule.lhs().nont()), arc)
else:
assert rule.lhs().nont() == grammar.start()
arc = Arc(0, terminals.add_symbol(str(rules.object_index(rule))), make_weight(rule.weight()),
nonterminals.find(rule.rhs_nont(0)))
myfst.add_arc(myfst.start(), arc)
myfst.set_input_symbols(terminals)
myfst.set_output_symbols(terminals)
myfst.optimize(True)
return myfst, rules
def check_wellformed_lattice(lattice: pynini.Fst) -> None:
"""Raises an error if the lattice is empty.
Args:
lattice: A lattice FST.
Raises:
Error: Lattice is empty.
"""
if lattice.start() == pynini.NO_STATE_ID:
raise Error("Lattice is empty")
def total_weight(self, fst: pynini.Fst) -> float:
return float(pynini.shortestdistance(fst, reverse=True)[fst.start()])
