refactor PreviousTransitions

Author: bygu4

pyformlang/finite_automaton/deterministic_finite_automaton.py

@@ -2,52 +2,15 @@
 Representation of a deterministic finite automaton
 """
 
-from typing import Dict, List, Iterable, AbstractSet, Optional, Hashable, Any
-from numpy import empty
+from typing import Iterable, AbstractSet, Optional, Hashable, Any
 
 from .state import State
-from .symbol import Symbol
 from .deterministic_transition_function import DeterministicTransitionFunction
 from .epsilon_nfa import EpsilonNFA
 from .nondeterministic_finite_automaton import NondeterministicFiniteAutomaton
 from .hopcroft_processing_list import HopcroftProcessingList
 from .partition import Partition
-from .utils import to_state, to_symbol, to_single_state
-
-
-class PreviousTransitions:
-    """For internal usage"""
-
-    def __init__(self,
-                 states: AbstractSet[State],
-                 symbols: AbstractSet[Symbol]) -> None:
-        self._to_index_state: Dict[Optional[State], int] = {}
-        self._to_index_state[None] = 0
-        for i, state in enumerate(states):
-            self._to_index_state[state] = i + 1
-        self._to_index_symbol: Dict[Optional[Symbol], int] = {}
-        for i, symbol in enumerate(symbols):
-            self._to_index_symbol[symbol] = i
-        self._conversion = empty((len(states) + 1, len(symbols)),
-                                 dtype=object)
-
-    def add(self,
-            next0: Optional[State],
-            symbol: Symbol,
-            state: Optional[State]) -> None:
-        """ Internal """
-        i_next0 = self._to_index_state[next0]
-        i_symbol = self._to_index_symbol[symbol]
-        if self._conversion[i_next0, i_symbol] is None:
-            self._conversion[i_next0, i_symbol] = [state]
-        else:
-            self._conversion[i_next0, i_symbol].append(state)
-
-    def get(self, next0: State, symbol: Symbol) -> List[object]:
-        """ Internal """
-        i_next0 = self._to_index_state[next0]
-        i_symbol = self._to_index_symbol[symbol]
-        return self._conversion[i_next0, i_symbol] or []
+from .utils import to_state, to_symbol, to_single_state, PreviousTransitions
 
 
 class DeterministicFiniteAutomaton(NondeterministicFiniteAutomaton):
@@ -263,8 +226,6 @@ def _get_previous_transitions(self) -> PreviousTransitions:
             for symbol in self._input_symbols:
                 next0 = self._transition_function.get_next_state(state, symbol)
                 previous_transitions.add(next0, symbol, state)
-        for symbol in self._input_symbols:
-            previous_transitions.add(None, symbol, None)
         return previous_transitions
 
     def minimize(self) -> "DeterministicFiniteAutomaton":

pyformlang/finite_automaton/utils.py

@@ -1,6 +1,7 @@
 """ Utility for finite automata """
 
-from typing import Iterable, Hashable
+from typing import Dict, List, AbstractSet, Iterable, Optional, Hashable
+from numpy import empty
 
 from .state import State
 from .symbol import Symbol
@@ -56,3 +57,40 @@ def to_single_state(l_states: Iterable[State]) -> State:
             values.append("TRASH")
     values = sorted(values)
     return State(";".join(values))
+
+
+class PreviousTransitions:
+    """
+    Previous transitions for deterministic automata
+    minimization algorithm.
+    """
+
+    def __init__(self,
+                 states: AbstractSet[State],
+                 symbols: AbstractSet[Symbol]) -> None:
+        self._to_index_state: Dict[State, int] = {}
+        for i, state in enumerate(states):
+            self._to_index_state[state] = i + 1
+        self._to_index_symbol: Dict[Symbol, int] = {}
+        for i, symbol in enumerate(symbols):
+            self._to_index_symbol[symbol] = i
+        self._conversion = empty((len(states) + 1, len(symbols)),
+                                 dtype=State)
+
+    def add(self,
+            next0: Optional[State],
+            symbol: Symbol,
+            state: State) -> None:
+        """ Internal """
+        i_next0 = self._to_index_state[next0] if next0 else 0
+        i_symbol = self._to_index_symbol[symbol]
+        if self._conversion[i_next0, i_symbol] is None:
+            self._conversion[i_next0, i_symbol] = [state]
+        else:
+            self._conversion[i_next0, i_symbol].append(state)
+
+    def get(self, next0: Optional[State], symbol: Symbol) -> List[State]:
+        """ Internal """
+        i_next0 = self._to_index_state[next0] if next0 else 0
+        i_symbol = self._to_index_symbol[symbol]
+        return self._conversion[i_next0, i_symbol] or []