def lattice_to_one_top_string(lattice: pynini.Fst,
token_type: Optional[pynini.TokenType] = None
) -> str:
"""Returns the top string in the lattice, raising an error if there's a tie.
Given a pruned DFA of output strings (such as produced by lattice_to_dfa
with optimal_only), extracts a single top string, raising an error if there's
a tie.
Args:
lattice: Epsilon-free deterministic finite acceptor.
token_type: Optional output token type, or symbol table.
Returns:
The top string.
Raises:
Error: Multiple top rewrites found.
"""
spaths = lattice.paths(output_token_type=token_type)
output = spaths.ostring()
spaths.next()
if not spaths.done():
raise Error("Multiple top rewrites found: "
f"{output} and {spaths.ostring()} (weight: {spaths.weight()})")
return output
def lattice_to_strings(
lattice: pynini.Fst,
token_type: Optional[pynini.TokenType] = None) -> List[str]:
"""Returns tuple of output strings.
Args:
lattice: Epsilon-free acyclic WFSA.
token_type: Optional output token type, or symbol table.
Returns:
An list of output strings.
"""
return list(lattice.paths(output_token_type=token_type).ostrings())
def _olabels_iter(f: pynini.Fst) -> Iterator[List[int]]:
it = f.paths()
while not it.done():
yield it.olabels()
it.next()