add remove_transition method for pda, update tests

Author: bygu4

pyformlang/fcfg/__init__.py

@@ -15,7 +15,8 @@
 
 """
 
-from .fcfg import FCFG, CFGObject, Variable, Terminal, Epsilon, ParseTree
+from .fcfg import FCFG, CFGObject, \
+    Variable, Terminal, Epsilon, ParseTree, NotParsableException
 from .feature_production import FeatureProduction
 from .feature_structure import FeatureStructure, \
     ContentAlreadyExistsException, \
@@ -31,6 +32,7 @@
            "Terminal",
            "Epsilon",
            "ParseTree",
+           "NotParsableException",
            "ContentAlreadyExistsException",
            "FeatureStructuresNotCompatibleException",
            "PathDoesNotExistsException"]

pyformlang/pda/pda.py

@@ -253,6 +253,24 @@ def add_transitions(self, transitions: Iterable[InputTransition]) -> None:
             self.add_transition(s_from, input_symbol, stack_from,
                                 s_to, stack_to)
 
+    def remove_transition(self,
+                          s_from: Hashable,
+                          input_symbol: Hashable,
+                          stack_from: Hashable,
+                          s_to: Hashable,
+                          stack_to: Iterable[Hashable]) -> None:
+        """ Remove the given transition from the PDA """
+        s_from = to_state(s_from)
+        input_symbol = to_symbol(input_symbol)
+        stack_from = to_stack_symbol(stack_from)
+        s_to = to_state(s_to)
+        stack_to = tuple(to_stack_symbol(x) for x in stack_to)
+        self._transition_function.remove_transition(s_from,
+                                                    input_symbol,
+                                                    stack_from,
+                                                    s_to,
+                                                    stack_to)
+
     def __call__(self,
                  s_from: Hashable,
                  input_symbol: Hashable,

pyformlang/pda/tests/test_pda.py

@@ -388,3 +388,32 @@ def test_object_eq(self):
         assert StackSymbol("ABC") != Symbol("ABC")
         assert State("ABC") != FAState("ABC")
         assert Symbol("s") != Terminal("s")
+
+    def test_contains(self, pda_example: PDA):
+        """ Tests the transition containment checks """
+        pda = pda_example
+        assert ("q1", "1", "Z1", "q2", []) in pda
+        assert ("q0", "epsilon", "Z1", "q2", tuple()) in pda
+        assert ("a", "b", "c", "d", ["e"]) not in pda
+        pda.add_transition("q1", "1", "Z1", "q5", ["a"])
+        assert ("q1", "1", "Z1", "q5", ["a"]) in pda
+
+    def test_remove_transition(self, pda_example: PDA):
+        """ Tests the pda transition removal """
+        pda = pda_example
+        assert ("q0", "0", "Z0", "q1", ("Z1", "Z0")) in pda
+        pda.remove_transition("q0", "0", "Z0", "q1", ("Z1", "Z0"))
+        assert ("q0", "0", "Z0", "q1", ("Z1", "Z0")) not in pda
+        pda.remove_transition("q0", "0", "Z0", "q1", ("Z1", "Z0"))
+        assert ("q0", "0", "Z0", "q1", ("Z1", "Z0")) not in pda
+        pda.remove_transition("a", "b", "c", "d", ["e"])
+        assert pda.get_number_transitions() == 2
+
+    def test_iteration(self, pda_example: PDA):
+        """ Tests the iteration of pda transitions """
+        pda = pda_example
+        transitions = list(iter(pda))
+        assert (("q0", "0", "Z0"), ("q1", ("Z1", "Z0"))) in transitions
+        assert (("q1", "1", "Z1"), ("q2", tuple())) in transitions
+        assert (("q0", "epsilon", "Z1"), ("q2", tuple())) in transitions
+        assert len(transitions) == 3

pyformlang/pda/transition_function.py

@@ -56,6 +56,17 @@ def add_transition(self,
         else:
             self._transitions[temp_in] = {temp_out}
 
+    def remove_transition(self,
+                          s_from: State,
+                          input_symbol: Symbol,
+                          stack_from: StackSymbol,
+                          s_to: State,
+                          stack_to: Tuple[StackSymbol, ...]) -> None:
+        """ Remove the given transition from the function """
+        key = (s_from, input_symbol, stack_from)
+        if key in self._transitions:
+            self._transitions[key].discard((s_to, stack_to))
+
     def copy(self) -> "TransitionFunction":
         """ Copy the current transition function