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Successors length limits #230

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Jun 28, 2024
Merged

Successors length limits #230

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59 changes: 55 additions & 4 deletions automata/fa/dfa.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1287,6 +1287,8 @@ def predecessor(
*,
strict: bool = True,
key: Optional[Callable[[Any], Any]] = None,
min_length: int = 0,
max_length: Optional[int] = None,
) -> Optional[str]:
"""
Returns the first string accepted by the DFA that comes before
Expand All @@ -1302,6 +1304,10 @@ def predecessor(
key : Optional[Callable], default: None
Function for defining custom lexicographical ordering. Defaults to using
the standard string ordering.
min_length : int, default: 0
Limits generation to words with at least the given length.
max_length : Optional[int], default: None
Limits generation to words with at most the given length.

Returns
------
Expand All @@ -1314,7 +1320,13 @@ def predecessor(
Raised if the language accepted by self is infinite, as we cannot
generate predecessors in this case.
"""
for word in self.predecessors(input_str, strict=strict, key=key):
for word in self.predecessors(
input_str,
strict=strict,
key=key,
min_length=min_length,
max_length=max_length,
):
return word
return None

Expand All @@ -1324,6 +1336,8 @@ def predecessors(
*,
strict: bool = True,
key: Optional[Callable[[Any], Any]] = None,
min_length: int = 0,
max_length: Optional[int] = None,
) -> Generator[str, None, None]:
"""
Generates all strings that come before the input string
Expand All @@ -1339,6 +1353,10 @@ def predecessors(
key : Optional[Callable], default: None
Function for defining custom lexicographical ordering. Defaults to using
the standard string ordering.
min_length : int, default: 0
Limits generation to words with at least the given length.
max_length : Optional[int], default: None
Limits generation to words with at most the given length.

Returns
------
Expand All @@ -1352,14 +1370,23 @@ def predecessors(
Raised if the language accepted by self is infinite, as we cannot
generate predecessors in this case.
"""
yield from self.successors(input_str, strict=strict, reverse=True, key=key)
yield from self.successors(
input_str,
strict=strict,
reverse=True,
key=key,
min_length=min_length,
max_length=max_length,
)

def successor(
self,
input_str: Optional[str],
*,
strict: bool = True,
key: Optional[Callable[[Any], Any]] = None,
min_length: int = 0,
max_length: Optional[int] = None,
) -> Optional[str]:
"""
Returns the first string accepted by the DFA that comes after
Expand All @@ -1375,13 +1402,23 @@ def successor(
key : Optional[Callable], default: None
Function for defining custom lexicographical ordering. Defaults to using
the standard string ordering.
min_length : int, default: 0
Limits generation to words with at least the given length.
max_length : Optional[int], default: None
Limits generation to words with at most the given length.

Returns
------
str
The first string accepted by the DFA lexicographically before input_string.
"""
for word in self.successors(input_str, strict=strict, key=key):
for word in self.successors(
input_str,
strict=strict,
key=key,
min_length=min_length,
max_length=max_length,
):
return word
return None

Expand All @@ -1392,6 +1429,8 @@ def successors(
strict: bool = True,
key: Optional[Callable[[Any], Any]] = None,
reverse: bool = False,
min_length: int = 0,
max_length: Optional[int] = None,
) -> Generator[str, None, None]:
"""
Generates all strings that come after the input string
Expand All @@ -1409,6 +1448,10 @@ def successors(
the standard string ordering.
reverse : bool, default: False
If True, then predecessors will be generated instead of successors.
min_length : int, default: 0
Limits generation to words with at least the given length.
max_length : Optional[int], default: None
Limits generation to words with at most the given length.

Returns
------
Expand Down Expand Up @@ -1457,6 +1500,8 @@ def successors(
if (
not reverse
and should_yield
and min_length <= len(char_stack)
and (max_length is None or len(char_stack) <= max_length)
and candidate == first_symbol
and state in self.final_states
):
Expand All @@ -1467,7 +1512,9 @@ def successors(
else self._get_next_current_state(state, candidate)
)
# Traverse to child if candidate is viable
if candidate_state in coaccessible_nodes:
if candidate_state in coaccessible_nodes and (
max_length is None or len(char_stack) < max_length
):
state_stack.append(candidate_state)
char_stack.append(cast(str, candidate))
candidate = first_symbol
Expand All @@ -1476,6 +1523,8 @@ def successors(
if (
reverse
and should_yield
and min_length <= len(char_stack)
and (max_length is None or len(char_stack) <= max_length)
and candidate is None
and state in self.final_states
):
Expand All @@ -1491,6 +1540,8 @@ def successors(
if (
reverse
and should_yield
and min_length <= len(char_stack)
and (max_length is None or len(char_stack) <= max_length)
and candidate is None
and state in self.final_states
):
Expand Down
11 changes: 11 additions & 0 deletions tests/test_dfa.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1887,6 +1887,9 @@ def test_predecessor(self, as_partial: bool) -> None:
actual = list(dfa.predecessors("010", strict=False))

self.assertEqual(dfa.predecessor("000"), "00")
self.assertEqual(dfa.predecessor("000", max_length=1), "0")
self.assertEqual(dfa.predecessor("0", min_length=2), None)
self.assertEqual(dfa.predecessor("0000", min_length=2, max_length=3), "000")
self.assertEqual(dfa.predecessor("0100"), "010")
self.assertEqual(dfa.predecessor("1"), "010101111111101011010100")
self.assertEqual(
Expand Down Expand Up @@ -1923,6 +1926,10 @@ def test_successor(self, as_partial: bool) -> None:
self.assertIsNone(dfa.successor("110"))
self.assertIsNone(dfa.successor("111111110101011"))

self.assertEqual(dfa.successor("", min_length=3), "000")
self.assertEqual(dfa.successor("", min_length=4), "010101111111101011010100")
self.assertEqual(dfa.successor("010", max_length=6), "100")

infinite_dfa = DFA.from_nfa(NFA.from_regex("0*1*"))
self.assertEqual(infinite_dfa.successor(""), "0")
self.assertEqual(infinite_dfa.successor("0"), "00")
Expand All @@ -1933,6 +1940,10 @@ def test_successor(self, as_partial: bool) -> None:
self.assertEqual(infinite_dfa.successor("1"), "11")
self.assertEqual(infinite_dfa.successor(100 * "0"), 101 * "0")
self.assertEqual(infinite_dfa.successor(100 * "1"), 101 * "1")
self.assertEqual(infinite_dfa.successor("", min_length=5), "00000")
self.assertEqual(infinite_dfa.successor("000", min_length=5), "00000")
self.assertEqual(infinite_dfa.successor("1", min_length=5), "11111")
self.assertEqual(infinite_dfa.successor("1111", max_length=4), None)

@params(True, False)
def test_successor_and_predecessor(self, as_partial: bool) -> None:
Expand Down
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