Add pairwise helper function (#170)

automata/base/utils.py

@@ -2,7 +2,7 @@
 """Miscellaneous utility functions and classes."""
 
 from collections import defaultdict
-from itertools import count
+from itertools import count, tee, zip_longest
 from typing import Any, Callable, Dict, Generic, Iterable, List, Set, Tuple, TypeVar
 
 from frozendict import frozendict
@@ -106,3 +106,14 @@ def refine(self, S: Iterable[T]) -> List[Tuple[int, int]]:
                 output.append((id(AintS), Aid))
 
         return output
+
+
+def pairwise(iterable: Iterable[T], final_none: bool = False) -> Iterable[Tuple[T, T]]:
+    """Based on https://docs.python.org/3/library/itertools.html#itertools.pairwise"""
+    a, b = tee(iterable)
+    next(b, None)
+
+    if final_none:
+        return zip_longest(a, b)
+
+    return zip(a, b)

automata/fa/dfa.py

@@ -32,7 +32,7 @@
 import automata.base.exceptions as exceptions
 import automata.fa.fa as fa
 import automata.fa.nfa as nfa
-from automata.base.utils import PartitionRefinement, get_renaming_function
+from automata.base.utils import PartitionRefinement, get_renaming_function, pairwise
 
 DFAStateT = fa.FAStateT
 
@@ -1072,8 +1072,7 @@ def successors(
         include_input = not strict
         sorted_symbols = sorted(self.input_symbols, reverse=reverse, key=key)
         symbol_succ: Dict[str, Optional[str]] = {
-            symbol_a: symbol_b
-            for symbol_a, symbol_b in zip(sorted_symbols, sorted_symbols[1:])
+            symbol_a: symbol_b for symbol_a, symbol_b in pairwise(sorted_symbols)
         }
         symbol_succ[sorted_symbols[-1]] = None
         # Special case for None
@@ -1757,7 +1756,11 @@ def _get_input_path(
         """
 
         state_history = list(self.read_input_stepwise(input_str, ignore_rejection=True))
-        path = list(zip(state_history, state_history[1:], input_str))
+
+        path = [
+            (*state_pair, char)
+            for state_pair, char in zip(pairwise(state_history), input_str)
+        ]
 
         last_state = state_history[-1] if state_history else self.initial_state
         accepted = last_state in self.final_states

automata/regex/parser.py

@@ -5,13 +5,13 @@
 import copy
 import re
 from collections import deque
-from itertools import chain, count, product, repeat, zip_longest
+from itertools import chain, count, product, repeat
 from typing import AbstractSet, Deque, Dict, Iterable, List, Optional, Set, Tuple, Type
 
 from typing_extensions import NoReturn, Self
 
 import automata.base.exceptions as exceptions
-from automata.base.utils import get_renaming_function
+from automata.base.utils import get_renaming_function, pairwise
 from automata.regex.lexer import Lexer, Token
 from automata.regex.postfix import (
     InfixOperator,
@@ -515,7 +515,7 @@ def add_concat_and_empty_string_tokens(
     # Pairs of tokens to insert empty string literals between
     empty_string_pairs = [(LeftParen, RightParen)]
 
-    for curr_token, next_token in zip_longest(token_list, token_list[1:]):
+    for curr_token, next_token in pairwise(token_list, True):
         final_token_list.append(curr_token)
 
         if next_token is not None:

automata/regex/postfix.py

@@ -3,8 +3,8 @@
 
 import abc
 from collections import deque
-from itertools import zip_longest
-from typing import Deque, List, Optional, Tuple, TypeVar, cast
+from itertools import chain, zip_longest
+from typing import Deque, Iterable, List, Optional, Tuple, TypeVar, cast
 
 import automata.base.exceptions as exceptions
 from automata.regex.lexer import Token
@@ -75,7 +75,7 @@ def __repr__(self) -> str:
 def validate_tokens(token_list: List[Token]) -> None:
     """Validate the inputted tokens list (in infix ordering)."""
 
-    token_list_prev: List[Optional[Token]] = [None] + token_list
+    token_list_prev: Iterable[Optional[Token]] = chain([None], token_list)
 
     paren_counter = 0