Improve logic and performance

lark/parsers/lalr_analysis.py

@@ -91,9 +91,7 @@ def from_ParseTable(cls, parse_table):
 def digraph(X, R, G):
     F = {}
     S = []
-    N = {}
-    for x in X:
-        N[x] = 0
+    N = dict.fromkeys(X, 0)
     for x in X:
         # this is always true for the first iteration, but N[x] may be updated in traverse below
         if N[x] == 0:
@@ -247,9 +245,7 @@ def compute_lalr1_states(self):
         m = {}
         reduce_reduce = []
         for state in self.lr0_states:
-            actions = {}
-            for la, next_state in state.transitions.items():
-                actions[la] = (Shift, next_state.closure)
+            actions = {la: (Shift, next_state.closure) for la, next_state in state.transitions.items()}
             for la, rules in state.lookaheads.items():
                 if len(rules) > 1:
                     # Try to resolve conflict based on priority

lark/utils.py

@@ -1,6 +1,7 @@
 import unicodedata
 import os
 from functools import reduce
+from itertools import product
 from collections import deque
 from typing import Callable, Iterator, List, Optional, Tuple, Type, TypeVar, Union, Dict, Any, Sequence
 
@@ -25,9 +26,9 @@ def classify(seq: Sequence, key: Optional[Callable] = None, value: Optional[Call
     for item in seq:
         k = key(item) if (key is not None) else item
         v = value(item) if (value is not None) else item
-        if k in d:
+        try:
             d[k].append(v)
-        else:
+        except KeyError:
             d[k] = [v]
     return d
 
@@ -228,9 +229,7 @@ def combine_alternatives(lists):
     if not lists:
         return [[]]
     assert all(l for l in lists), lists
-    init = [[x] for x in lists[0]]
-    return reduce(lambda a,b: [i+[j] for i in a for j in b], lists[1:], init)
-
+    return list(product(*lists))
 
 try:
     import atomicwrites
@@ -268,15 +267,8 @@ def __repr__(self):
 
 
 def classify_bool(seq: Sequence, pred: Callable) -> Any:
-    true_elems = []
     false_elems = []
-
-    for elem in seq:
-        if pred(elem):
-            true_elems.append(elem)
-        else:
-            false_elems.append(elem)
-
+    true_elems = [elem for elem in seq if pred(elem) or false_elems.append(elem)]  # type: ignore[func-returns-value]
     return true_elems, false_elems