Merge branch 'regex'

.github/workflows/tests.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install -r nearley-requirements.txt
+          pip install -r test-requirements.txt
       - name: Run tests
         run: |
           python -m tests

docs/classes.md

@@ -70,6 +70,8 @@ Useful for caching and multiprocessing.
 
 **g_regex_flags** - Flags that are applied to all terminals (both regex and strings)
 
+**regex** - Use the `regex` library instead of the built-in `re` module (See below)
+
 **keep_all_tokens** - Prevent the tree builder from automagically removing "punctuation" tokens (default: False)
 
 **cache** - Cache the results of the Lark grammar analysis, for x2 to x3 faster loading. LALR only for now.
@@ -94,13 +96,35 @@ Useful for caching and multiprocessing.
 - "resolve": The parser will automatically choose the simplest derivation (it chooses consistently: greedy for tokens, non-greedy for rules)
 - "explicit": The parser will return all derivations wrapped in "_ambig" tree nodes (i.e. a forest).
 
-#### Domain Specific
+#### Misc.
 
 - **postlex** - Lexer post-processing (Default: None) Only works with the standard and contextual lexers.
 - **priority** - How priorities should be evaluated - auto, none, normal, invert (Default: auto)
 - **lexer_callbacks** - Dictionary of callbacks for the lexer. May alter tokens during lexing. Use with caution.
 - **edit_terminals** - A callback
 
+
+#### Using Unicode character classes with `regex`
+Python's builtin `re` module has a few persistent known bugs and also won't parse
+advanced regex features such as character classes.
+With `pip install lark-parser[regex]`, the `regex` module will be installed alongside `lark`
+and can act as a drop-in replacement to `re`.
+
+Any instance of `Lark` instantiated with `regex=True` will now use the `regex` module
+instead of `re`. For example, we can now use character classes to match PEP-3131 compliant Python identifiers.
+```python
+from lark import Lark
+>>> g = Lark(r"""
+                    ?start: NAME
+                    NAME: ID_START ID_CONTINUE*
+                    ID_START: /[\p{Lu}\p{Ll}\p{Lt}\p{Lm}\p{Lo}\p{Nl}_]+/
+                    ID_CONTINUE: ID_START | /[\p{Mn}\p{Mc}\p{Nd}\p{Pc}·]+/
+                """, regex=True)
+
+>>> g.parse('வணக்கம்')
+'வணக்கம்'
+
+```
 ----
 
 ## Tree

lark-stubs/lark.pyi

@@ -23,6 +23,7 @@ class LarkOptions:
     transformer: Optional[Transformer]
     postlex: Optional[PostLex]
     ambiguity: str
+    regex: bool
     debug: bool
     keep_all_tokens: bool
     propagate_positions: bool
@@ -48,6 +49,7 @@ class Lark:
         transformer: Optional[Transformer] = None,
         postlex: Optional[PostLex] = None,
         ambiguity: Literal["explicit", "resolve"] = "resolve",
+        regex: bool = False,
         debug: bool = False,
         keep_all_tokens: bool = False,
         propagate_positions: bool = False,

lark-stubs/lexer.pyi

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-
+from types import ModuleType
 from typing import (
     TypeVar, Type, Tuple, List, Dict, Iterator, Collection, Callable, Optional,
     Pattern as REPattern,
@@ -107,10 +107,12 @@ class TraditionalLexer(Lexer):
     user_callbacks: Dict[str, _Callback]
     callback: Dict[str, _Callback]
     mres: List[Tuple[REPattern, Dict[int, str]]]
+    re: ModuleType
 
     def __init__(
         self,
         terminals: Collection[TerminalDef],
+        re_: ModuleType,
         ignore: Collection[str] = ...,
         user_callbacks: Dict[str, _Callback] = ...,
         g_regex_flags: int = ...
@@ -135,6 +137,7 @@ class ContextualLexer(Lexer):
         self,
         terminals: Collection[TerminalDef],
         states: Dict[str, Collection[str]],
+        re_: ModuleType,
         ignore: Collection[str] = ...,
         always_accept: Collection[str] = ...,
         user_callbacks: Dict[str, _Callback] = ...,

lark/lark.py

@@ -14,6 +14,12 @@ from .parse_tree_builder import ParseTreeBuilder
 from .parser_frontends import get_frontend
 from .grammar import Rule
 
+import re
+try:
+    import regex
+except ImportError:
+    regex = None
+
 ###{standalone
 
 class LarkOptions(Serialize):
@@ -34,6 +40,7 @@ class LarkOptions(Serialize):
                          When `False`,  `[]` behaves like the `?` operator,
                              and returns no value at all.
                          (default=`False`. Recommended to set to `True`)
+    regex - When True, uses the `regex` module instead of the stdlib `re`.
     cache - Cache the results of the Lark grammar analysis, for x2 to x3 faster loading.
             LALR only for now.
         When `False`, does nothing (default)
@@ -92,6 +99,7 @@ class LarkOptions(Serialize):
         'start': 'start',
         'priority': 'auto',
         'ambiguity': 'auto',
+        'regex': False,
         'propagate_positions': False,
         'lexer_callbacks': {},
         'maybe_placeholders': False,
@@ -154,6 +162,16 @@ class Lark(Serialize):
 
         self.options = LarkOptions(options)
 
+        # Set regex or re module
+        use_regex = self.options.regex
+        if use_regex:
+            if regex:
+                self.re = regex
+            else:
+                raise ImportError('`regex` module must be installed if calling `Lark(regex=True)`.')
+        else:
+            self.re = re
+
         # Some, but not all file-like objects have a 'name' attribute
         try:
             self.source = grammar.name
@@ -225,7 +243,7 @@ class Lark(Serialize):
         assert self.options.ambiguity in ('resolve', 'explicit', 'auto', )
 
         # Parse the grammar file and compose the grammars (TODO)
-        self.grammar = load_grammar(grammar, self.source)
+        self.grammar = load_grammar(grammar, self.source, self.re)
 
         # Compile the EBNF grammar into BNF
         self.terminals, self.rules, self.ignore_tokens = self.grammar.compile(self.options.start)
@@ -286,7 +304,7 @@ class Lark(Serialize):
     def _build_parser(self):
         self._prepare_callbacks()
         parser_conf = ParserConf(self.rules, self._callbacks, self.options.start)
-        return self.parser_class(self.lexer_conf, parser_conf, options=self.options)
+        return self.parser_class(self.lexer_conf, parser_conf, self.re, options=self.options)
 
     def save(self, f):
         data, m = self.memo_serialize([TerminalDef, Rule])
@@ -313,10 +331,11 @@ class Lark(Serialize):
         if postlex is not None:
             options['postlex'] = postlex
         self.options = LarkOptions.deserialize(options, memo)
+        self.re = regex if self.options.regex else re
         self.rules = [Rule.deserialize(r, memo) for r in data['rules']]
         self.source = '<deserialized>'
         self._prepare_callbacks()
-        self.parser = self.parser_class.deserialize(data['parser'], memo, self._callbacks, self.options.postlex)
+        self.parser = self.parser_class.deserialize(data['parser'], memo, self._callbacks, self.options.postlex, self.re)
         return self
 
     @classmethod

lark/lexer.py

@@ -230,7 +230,7 @@ class CallChain:
 
 
 
-def _create_unless(terminals, g_regex_flags):
+def _create_unless(terminals, g_regex_flags, re_):
     tokens_by_type = classify(terminals, lambda t: type(t.pattern))
     assert len(tokens_by_type) <= 2, tokens_by_type.keys()
     embedded_strs = set()
@@ -241,19 +241,19 @@ def _create_unless(terminals, g_regex_flags):
             if strtok.priority > retok.priority:
                 continue
             s = strtok.pattern.value
-            m = re.match(retok.pattern.to_regexp(), s, g_regex_flags)
+            m = re_.match(retok.pattern.to_regexp(), s, g_regex_flags)
             if m and m.group(0) == s:
                 unless.append(strtok)
                 if strtok.pattern.flags <= retok.pattern.flags:
                     embedded_strs.add(strtok)
         if unless:
-            callback[retok.name] = UnlessCallback(build_mres(unless, g_regex_flags, match_whole=True))
+            callback[retok.name] = UnlessCallback(build_mres(unless, g_regex_flags, re_, match_whole=True))
 
     terminals = [t for t in terminals if t not in embedded_strs]
     return terminals, callback
 
 
-def _build_mres(terminals, max_size, g_regex_flags, match_whole):
+def _build_mres(terminals, max_size, g_regex_flags, match_whole, re_):
     # Python sets an unreasonable group limit (currently 100) in its re module
     # Worse, the only way to know we reached it is by catching an AssertionError!
     # This function recursively tries less and less groups until it's successful.
@@ -261,17 +261,17 @@ def _build_mres(terminals, max_size, g_regex_flags, match_whole):
     mres = []
     while terminals:
         try:
-            mre = re.compile(u'|'.join(u'(?P<%s>%s)'%(t.name, t.pattern.to_regexp()+postfix) for t in terminals[:max_size]), g_regex_flags)
+            mre = re_.compile(u'|'.join(u'(?P<%s>%s)'%(t.name, t.pattern.to_regexp()+postfix) for t in terminals[:max_size]), g_regex_flags)
         except AssertionError:  # Yes, this is what Python provides us.. :/
-            return _build_mres(terminals, max_size//2, g_regex_flags, match_whole)
+            return _build_mres(terminals, max_size//2, g_regex_flags, match_whole, re_)
 
         # terms_from_name = {t.name: t for t in terminals[:max_size]}
         mres.append((mre, {i:n for n,i in mre.groupindex.items()} ))
         terminals = terminals[max_size:]
     return mres
 
-def build_mres(terminals, g_regex_flags, match_whole=False):
-    return _build_mres(terminals, len(terminals), g_regex_flags, match_whole)
+def build_mres(terminals, g_regex_flags, re_, match_whole=False):
+    return _build_mres(terminals, len(terminals), g_regex_flags, match_whole, re_)
 
 def _regexp_has_newline(r):
     r"""Expressions that may indicate newlines in a regexp:
@@ -294,16 +294,17 @@ class Lexer(object):
 
 class TraditionalLexer(Lexer):
 
-    def __init__(self, terminals, ignore=(), user_callbacks={}, g_regex_flags=0):
+    def __init__(self, terminals, re_, ignore=(), user_callbacks={}, g_regex_flags=0):
         assert all(isinstance(t, TerminalDef) for t in terminals), terminals
 
         terminals = list(terminals)
 
+        self.re = re_
         # Sanitization
         for t in terminals:
             try:
-                re.compile(t.pattern.to_regexp(), g_regex_flags)
-            except re.error:
+                self.re.compile(t.pattern.to_regexp(), g_regex_flags)
+            except self.re.error:
                 raise LexError("Cannot compile token %s: %s" % (t.name, t.pattern))
 
             if t.pattern.min_width == 0:
@@ -321,7 +322,7 @@ class TraditionalLexer(Lexer):
         self.build(g_regex_flags)
 
     def build(self, g_regex_flags=0):
-        terminals, self.callback = _create_unless(self.terminals, g_regex_flags)
+        terminals, self.callback = _create_unless(self.terminals, g_regex_flags, re_=self.re)
         assert all(self.callback.values())
 
         for type_, f in self.user_callbacks.items():
@@ -331,7 +332,7 @@ class TraditionalLexer(Lexer):
             else:
                 self.callback[type_] = f
 
-        self.mres = build_mres(terminals, g_regex_flags)
+        self.mres = build_mres(terminals, g_regex_flags, self.re)
 
     def match(self, stream, pos):
         for mre, type_from_index in self.mres:
@@ -347,7 +348,8 @@ class TraditionalLexer(Lexer):
 
 class ContextualLexer(Lexer):
 
-    def __init__(self, terminals, states, ignore=(), always_accept=(), user_callbacks={}, g_regex_flags=0):
+    def __init__(self, terminals, states, re_, ignore=(), always_accept=(), user_callbacks={}, g_regex_flags=0):
+        self.re = re_
         tokens_by_name = {}
         for t in terminals:
             assert t.name not in tokens_by_name, t
@@ -362,12 +364,12 @@ class ContextualLexer(Lexer):
             except KeyError:
                 accepts = set(accepts) | set(ignore) | set(always_accept)
                 state_tokens = [tokens_by_name[n] for n in accepts if n and n in tokens_by_name]
-                lexer = TraditionalLexer(state_tokens, ignore=ignore, user_callbacks=user_callbacks, g_regex_flags=g_regex_flags)
+                lexer = TraditionalLexer(state_tokens, re_=self.re, ignore=ignore, user_callbacks=user_callbacks, g_regex_flags=g_regex_flags)
                 lexer_by_tokens[key] = lexer
 
             self.lexers[state] = lexer
 
-        self.root_lexer = TraditionalLexer(terminals, ignore=ignore, user_callbacks=user_callbacks, g_regex_flags=g_regex_flags)
+        self.root_lexer = TraditionalLexer(terminals, re_=self.re, ignore=ignore, user_callbacks=user_callbacks, g_regex_flags=g_regex_flags)
 
     def lex(self, stream, get_parser_state):
         parser_state = get_parser_state()

lark/load_grammar.py

@@ -616,7 +616,7 @@ class Grammar:
 
 
 _imported_grammars = {}
-def import_grammar(grammar_path, base_paths=[]):
+def import_grammar(grammar_path, re_, base_paths=[]):
     if grammar_path not in _imported_grammars:
         import_paths = base_paths + IMPORT_PATHS
         for import_path in import_paths:
@@ -624,7 +624,7 @@ def import_grammar(grammar_path, base_paths=[]):
                 joined_path = os.path.join(import_path, grammar_path)
                 with open(joined_path, encoding='utf8') as f:
                     text = f.read()
-                grammar = load_grammar(text, joined_path)
+                grammar = load_grammar(text, joined_path, re_)
                 _imported_grammars[grammar_path] = grammar
                 break
         else:
@@ -755,7 +755,8 @@ def _find_used_symbols(tree):
               for t in x.scan_values(lambda t: t.type in ('RULE', 'TERMINAL'))}
 
 class GrammarLoader:
-    def __init__(self):
+    def __init__(self, re_):
+        self.re = re_
         terminals = [TerminalDef(name, PatternRE(value)) for name, value in TERMINALS.items()]
 
         rules = [options_from_rule(name, None, x) for name, x in  RULES.items()]
@@ -764,7 +765,7 @@ class GrammarLoader:
         lexer_conf = LexerConf(terminals, ['WS', 'COMMENT'])
 
         parser_conf = ParserConf(rules, callback, ['start'])
-        self.parser = LALR_TraditionalLexer(lexer_conf, parser_conf)
+        self.parser = LALR_TraditionalLexer(lexer_conf, parser_conf, re_)
 
         self.canonize_tree = CanonizeTree()
 
@@ -862,7 +863,7 @@ class GrammarLoader:
         # import grammars
         for dotted_path, (base_paths, aliases) in imports.items():
             grammar_path = os.path.join(*dotted_path) + EXT
-            g = import_grammar(grammar_path, base_paths=base_paths)
+            g = import_grammar(grammar_path, self.re, base_paths=base_paths)
             new_td, new_rd = import_from_grammar_into_namespace(g, '__'.join(dotted_path), aliases)
 
             term_defs += new_td
@@ -942,4 +943,5 @@ class GrammarLoader:
 
 
 
-load_grammar = GrammarLoader().load_grammar
+def load_grammar(grammar, source, re_):
+    return GrammarLoader(re_).load_grammar(grammar, source)

lark/parser_frontends.py

@@ -1,4 +1,3 @@
-import re
 from functools import partial
 
 from .utils import get_regexp_width, Serialize
@@ -63,14 +62,16 @@ class WithLexer(_ParserFrontend):
     __serialize_fields__ = 'parser', 'lexer_conf', 'start'
     __serialize_namespace__ = LexerConf,
 
-    def __init__(self, lexer_conf, parser_conf, options=None):
+    def __init__(self, lexer_conf, parser_conf, re_, options=None):
         self.lexer_conf = lexer_conf
         self.start = parser_conf.start
         self.postlex = lexer_conf.postlex
+        self.re = re_
 
     @classmethod
-    def deserialize(cls, data, memo, callbacks, postlex):
+    def deserialize(cls, data, memo, callbacks, postlex, re_):
         inst = super(WithLexer, cls).deserialize(data, memo)
+        inst.re = re_
         inst.postlex = postlex
         inst.parser = LALR_Parser.deserialize(inst.parser, memo, callbacks)
         inst.init_lexer()
@@ -88,13 +89,14 @@ class WithLexer(_ParserFrontend):
         return self._parse(token_stream, start)
 
     def init_traditional_lexer(self):
-        self.lexer = TraditionalLexer(self.lexer_conf.tokens, ignore=self.lexer_conf.ignore, user_callbacks=self.lexer_conf.callbacks, g_regex_flags=self.lexer_conf.g_regex_flags)
+        self.lexer = TraditionalLexer(self.lexer_conf.tokens, re_=self.re, ignore=self.lexer_conf.ignore, user_callbacks=self.lexer_conf.callbacks, g_regex_flags=self.lexer_conf.g_regex_flags)
 
 class LALR_WithLexer(WithLexer):
-    def __init__(self, lexer_conf, parser_conf, options=None):
+    def __init__(self, lexer_conf, parser_conf, re_, options=None):
         debug = options.debug if options else False
+        self.re = re_
         self.parser = LALR_Parser(parser_conf, debug=debug)
-        WithLexer.__init__(self, lexer_conf, parser_conf, options)
+        WithLexer.__init__(self, lexer_conf, parser_conf, re_, options)
 
         self.init_lexer()
 
@@ -110,6 +112,7 @@ class LALR_ContextualLexer(LALR_WithLexer):
         states = {idx:list(t.keys()) for idx, t in self.parser._parse_table.states.items()}
         always_accept = self.postlex.always_accept if self.postlex else ()
         self.lexer = ContextualLexer(self.lexer_conf.tokens, states,
+                                     re_=self.re,
                                      ignore=self.lexer_conf.ignore,
                                      always_accept=always_accept,
                                      user_callbacks=self.lexer_conf.callbacks,
@@ -126,11 +129,11 @@ class LALR_ContextualLexer(LALR_WithLexer):
 ###}
 
 class LALR_CustomLexer(LALR_WithLexer):
-    def __init__(self, lexer_cls, lexer_conf, parser_conf, options=None):
-        self.lexer = lexer_cls(lexer_conf)
+    def __init__(self, lexer_cls, lexer_conf, parser_conf, re_, options=None):
+        self.lexer = lexer_cls(lexer_conf, re_=re_)
         debug = options.debug if options else False
         self.parser = LALR_Parser(parser_conf, debug=debug)
-        WithLexer.__init__(self, lexer_conf, parser_conf, options)
+        WithLexer.__init__(self, lexer_conf, parser_conf, re_, options)
 
 
 def tokenize_text(text):
@@ -143,8 +146,8 @@ def tokenize_text(text):
         yield Token('CHAR', ch, line=line, column=i - col_start_pos)
 
 class Earley(WithLexer):
-    def __init__(self, lexer_conf, parser_conf, options=None):
-        WithLexer.__init__(self, lexer_conf, parser_conf, options)
+    def __init__(self, lexer_conf, parser_conf, re_, options=None):
+        WithLexer.__init__(self, lexer_conf, parser_conf, re_, options)
         self.init_traditional_lexer()
 
         resolve_ambiguity = options.ambiguity == 'resolve'
@@ -156,7 +159,9 @@ class Earley(WithLexer):
 
 
 class XEarley(_ParserFrontend):
-    def __init__(self, lexer_conf, parser_conf, options=None, **kw):
+    def __init__(self, lexer_conf, parser_conf, re_, options=None, **kw):
+        self.re = re_
+
         self.token_by_name = {t.name:t for t in lexer_conf.tokens}
         self.start = parser_conf.start
 
@@ -188,7 +193,7 @@ class XEarley(_ParserFrontend):
                 if width == 0:
                     raise ValueError("Dynamic Earley doesn't allow zero-width regexps", t)
 
-            self.regexps[t.name] = re.compile(regexp, lexer_conf.g_regex_flags)
+            self.regexps[t.name] = self.re.compile(regexp, lexer_conf.g_regex_flags)
 
     def parse(self, text, start):
         return self._parse(text, start)
@@ -201,8 +206,8 @@ class XEarley_CompleteLex(XEarley):
 
 class CYK(WithLexer):
 
-    def __init__(self, lexer_conf, parser_conf, options=None):
-        WithLexer.__init__(self, lexer_conf, parser_conf, options)
+    def __init__(self, lexer_conf, parser_conf, re_, options=None):
+        WithLexer.__init__(self, lexer_conf, parser_conf, re_, options)
         self.init_traditional_lexer()
 
         self._analysis = GrammarAnalyzer(parser_conf)

lark/utils.py

@@ -165,16 +165,31 @@ def smart_decorator(f, create_decorator):
     else:
         return create_decorator(f.__func__.__call__, True)
 
+try:
+    import regex
+except ImportError:
+    regex = None
+
 import sys, re
 Py36 = (sys.version_info[:2] >= (3, 6))
 
 import sre_parse
 import sre_constants
-def get_regexp_width(regexp):
+categ_pattern = re.compile(r'\\p{[A-Za-z_]+}')
+def get_regexp_width(expr):
+    if regex:
+        # Since `sre_parse` cannot deal with Unicode categories of the form `\p{Mn}`, we replace these with
+        # a simple letter, which makes no difference as we are only trying to get the possible lengths of the regex
+        # match here below.
+        regexp_final = re.sub(categ_pattern, 'A', expr)
+    else:
+        if re.search(categ_pattern, expr):
+            raise ImportError('`regex` module must be installed in order to use Unicode categories.', expr)
+        regexp_final = expr
     try:
-        return [int(x) for x in sre_parse.parse(regexp).getwidth()]
+        return [int(x) for x in sre_parse.parse(regexp_final).getwidth()]
     except sre_constants.error:
-        raise ValueError(regexp)
+        raise ValueError(expr)
 
 ###}
 
@@ -182,7 +197,7 @@ def get_regexp_width(regexp):
 def dedup_list(l):
     """Given a list (l) will removing duplicates from the list,
        preserving the original order of the list. Assumes that
-       the list entrie are hashable."""
+       the list entries are hashable."""
     dedup = set()
     return [ x for x in l if not (x in dedup or dedup.add(x))]
 

setup.py

@@ -1,4 +1,7 @@
-import re
+try:
+    import regex as re
+except ImportError:
+    import re
 from setuptools import find_packages, setup
 
 __version__ ,= re.findall('__version__ = "(.*)"', open('lark/__init__.py').read())
@@ -11,6 +14,10 @@ setup(
     requires = [],
     install_requires = [],
 
+    extras_require = {
+        "regex": ["regex"]
+    },
+
     package_data = {'': ['*.md', '*.lark'], 'lark-stubs': ['*.pyi']},
 
     test_suite = 'tests.__main__',

nearley-requirements.txt → test-requirements.txt

@@ -1 +1,2 @@
 Js2Py==0.68
+regex

tests/test_parser.py

@@ -20,6 +20,11 @@ from io import (
 
 logging.basicConfig(level=logging.INFO)
 
+try:
+    import regex
+except ImportError:
+    regex = None
+
 from lark.lark import Lark
 from lark.exceptions import GrammarError, ParseError, UnexpectedToken, UnexpectedInput, UnexpectedCharacters
 from lark.tree import Tree
@@ -548,8 +553,8 @@ class CustomLexer(Lexer):
     Purpose of this custom lexer is to test the integration,
     so it uses the traditionalparser as implementation without custom lexing behaviour.
     """
-    def __init__(self, lexer_conf):
-        self.lexer = TraditionalLexer(lexer_conf.tokens, ignore=lexer_conf.ignore, user_callbacks=lexer_conf.callbacks, g_regex_flags=lexer_conf.g_regex_flags)
+    def __init__(self, lexer_conf, re_):
+        self.lexer = TraditionalLexer(lexer_conf.tokens, re_, ignore=lexer_conf.ignore, user_callbacks=lexer_conf.callbacks, g_regex_flags=lexer_conf.g_regex_flags)
     def lex(self, *args, **kwargs):
         return self.lexer.lex(*args, **kwargs)
 
@@ -1784,6 +1789,23 @@ def _make_parser_test(LEXER, PARSER):
                 self.assertEqual(a.line, 1)
                 self.assertEqual(b.line, 2)
 
+        @unittest.skipIf(not regex or sys.version_info[0] == 2, 'Unicode and Python 2 do not place nicely together.')
+        def test_unicode_class(self):
+            "Tests that character classes from the `regex` module work correctly."
+            g = _Lark(r"""?start: NAME
+                           NAME: ID_START ID_CONTINUE*
+                           ID_START: /[\p{Lu}\p{Ll}\p{Lt}\p{Lm}\p{Lo}\p{Nl}_]+/
+                           ID_CONTINUE: ID_START | /[\p{Mn}\p{Mc}\p{Nd}\p{Pc}]+/""", regex=True)
+
+            self.assertEqual(g.parse('வணக்கம்'), 'வணக்கம்')
+
+        @unittest.skipIf(not regex or sys.version_info[0] == 2, 'Unicode and Python 2 do not place nicely together.')
+        def test_unicode_word(self):
+            "Tests that a persistent bug in the `re` module works when `regex` is enabled."
+            g = _Lark(r"""?start: NAME
+                           NAME: /[\w]+/
+                        """, regex=True)
+            self.assertEqual(g.parse('வணக்கம்'), 'வணக்கம்')
 
     _NAME = "Test" + PARSER.capitalize() + LEXER.capitalize()
     _TestParser.__name__ = _NAME

tox.ini

@@ -14,7 +14,7 @@ pypy3 = pypy3
 [testenv]
 whitelist_externals = git
 deps =
-    -rnearley-requirements.txt
+    -rtest-requirements.txt
 
 # to always force recreation and avoid unexpected side effects
 recreate=True