from __future__ import absolute_import
from lark.exceptions import ConfigurationError, assert_config
import sys, os, pickle, hashlib
from io import open
import tempfile
from warnings import warn
from .utils import STRING_TYPE, Serialize, SerializeMemoizer, FS, isascii, logger, ABC, abstractmethod
from .load_grammar import load_grammar, FromPackageLoader, Grammar, verify_used_files
from .tree import Tree
from .common import LexerConf, ParserConf
from .lexer import Lexer, TraditionalLexer, TerminalDef, LexerThread
from .parse_tree_builder import ParseTreeBuilder
from .parser_frontends import get_frontend, _get_lexer_callbacks
from .grammar import Rule
import re
try:
import regex
except ImportError:
regex = None
###{standalone
class LarkOptions(Serialize):
"""Specifies the options for Lark
"""
OPTIONS_DOC = """
**=== General Options ===**
start
The start symbol. Either a string, or a list of strings for multiple possible starts (Default: "start")
debug
Display debug information and extra warnings. Use only when debugging (default: False)
When used with Earley, it generates a forest graph as "sppf.png", if 'dot' is installed.
transformer
Applies the transformer to every parse tree (equivalent to applying it after the parse, but faster)
propagate_positions
Propagates (line, column, end_line, end_column) attributes into all tree branches.
Accepts ``False``, ``True``, or a callable, which will filter which nodes to ignore when propagating.
maybe_placeholders
When ``True``, the ``[]`` operator returns ``None`` when not matched.
When ``False``, ``[]`` behaves like the ``?`` operator, and returns no value at all.
(default= ``False``. Recommended to set to ``True``)
cache
Cache the results of the Lark grammar analysis, for x2 to x3 faster loading. LALR only for now.
- When ``False``, does nothing (default)
- When ``True``, caches to a temporary file in the local directory
- When given a string, caches to the path pointed by the string
regex
When True, uses the ``regex`` module instead of the stdlib ``re``.
g_regex_flags
Flags that are applied to all terminals (both regex and strings)
keep_all_tokens
Prevent the tree builder from automagically removing "punctuation" tokens (default: False)
tree_class
Lark will produce trees comprised of instances of this class instead of the default ``lark.Tree``.
**=== Algorithm Options ===**
parser
Decides which parser engine to use. Accepts "earley" or "lalr". (Default: "earley").
(there is also a "cyk" option for legacy)
lexer
Decides whether or not to use a lexer stage
- "auto" (default): Choose for me based on the parser
- "standard": Use a standard lexer
- "contextual": Stronger lexer (only works with parser="lalr")
- "dynamic": Flexible and powerful (only with parser="earley")
- "dynamic_complete": Same as dynamic, but tries *every* variation of tokenizing possible.
ambiguity
Decides how to handle ambiguity in the parse. Only relevant if parser="earley"
- "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).
- "forest": The parser will return the root of the shared packed parse forest.
**=== Misc. / Domain Specific Options ===**
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.
use_bytes
Accept an input of type ``bytes`` instead of ``str`` (Python 3 only).
edit_terminals
A callback for editing the terminals before parse.
import_paths
A List of either paths or loader functions to specify from where grammars are imported
source_path
Override the source of from where the grammar was loaded. Useful for relative imports and unconventional grammar loading
**=== End of Options ===**
"""
if __doc__:
__doc__ += OPTIONS_DOC
# Adding a new option needs to be done in multiple places:
# - In the dictionary below. This is the primary truth of which options `Lark.__init__` accepts
# - In the docstring above. It is used both for the docstring of `LarkOptions` and `Lark`, and in readthedocs
# - In `lark-stubs/lark.pyi`:
# - As attribute to `LarkOptions`
# - As parameter to `Lark.__init__`
# - Potentially in `_LOAD_ALLOWED_OPTIONS` below this class, when the option doesn't change how the grammar is loaded
# - Potentially in `lark.tools.__init__`, if it makes sense, and it can easily be passed as a cmd argument
_defaults = {
'debug': False,
'keep_all_tokens': False,
'tree_class': None,
'cache': False,
'postlex': None,
'parser': 'earley',
'lexer': 'auto',
'transformer': None,
'start': 'start',
'priority': 'auto',
'ambiguity': 'auto',
'regex': False,
'propagate_positions': False,
'lexer_callbacks': {},
'maybe_placeholders': False,
'edit_terminals': None,
'g_regex_flags': 0,
'use_bytes': False,
'import_paths': [],
'source_path': None,
}
def __init__(self, options_dict):
o = dict(options_dict)
options = {}
for name, default in self._defaults.items():
if name in o:
value = o.pop(name)
if isinstance(default, bool) and name not in ('cache', 'use_bytes', 'propagate_positions'):
value = bool(value)
else:
value = default
options[name] = value
if isinstance(options['start'], STRING_TYPE):
options['start'] = [options['start']]
self.__dict__['options'] = options
assert_config(self.parser, ('earley', 'lalr', 'cyk', None))
if self.parser == 'earley' and self.transformer:
raise ConfigurationError('Cannot specify an embedded transformer when using the Earley algorithm. '
'Please use your transformer on the resulting parse tree, or use a different algorithm (i.e. LALR)')
if o:
raise ConfigurationError("Unknown options: %s" % o.keys())
def __getattr__(self, name):
try:
return self.__dict__['options'][name]
except KeyError as e:
raise AttributeError(e)
def __setattr__(self, name, value):
assert_config(name, self.options.keys(), "%r isn't a valid option. Expected one of: %s")
self.options[name] = value
def serialize(self, memo):
return self.options
@classmethod
def deserialize(cls, data, memo):
return cls(data)
# Options that can be passed to the Lark parser, even when it was loaded from cache/standalone.
# These option are only used outside of `load_grammar`.
_LOAD_ALLOWED_OPTIONS = {'postlex', 'transformer', 'lexer_callbacks', 'use_bytes', 'debug', 'g_regex_flags', 'regex', 'propagate_positions', 'tree_class'}
_VALID_PRIORITY_OPTIONS = ('auto', 'normal', 'invert', None)
_VALID_AMBIGUITY_OPTIONS = ('auto', 'resolve', 'explicit', 'forest')
class PostLex(ABC):
@abstractmethod
def process(self, stream):
return stream
always_accept = ()
class Lark(Serialize):
"""Main interface for the library.
It's mostly a thin wrapper for the many different parsers, and for the tree constructor.
Parameters:
grammar: a string or file-object containing the grammar spec (using Lark's ebnf syntax)
options: a dictionary controlling various aspects of Lark.
Example:
>>> Lark(r'''start: "foo" ''')
Lark(...)
"""
def __init__(self, grammar, **options):
self.options = LarkOptions(options)
# Set regex or re module
use_regex = self.options.regex
if use_regex:
if regex:
re_module = regex
else:
raise ImportError('`regex` module must be installed if calling `Lark(regex=True)`.')
else:
re_module = re
# Some, but not all file-like objects have a 'name' attribute
if self.options.source_path is None:
try:
self.source_path = grammar.name
except AttributeError:
self.source_path = '<string>'
else:
self.source_path = self.options.source_path
# Drain file-like objects to get their contents
try:
read = grammar.read
except AttributeError:
pass
else:
grammar = read()
cache_fn = None
cache_md5 = None
if isinstance(grammar, STRING_TYPE):
self.source_grammar = grammar
if self.options.use_bytes:
if not isascii(grammar):
raise ConfigurationError("Grammar must be ascii only, when use_bytes=True")
if sys.version_info[0] == 2 and self.options.use_bytes != 'force':
raise ConfigurationError("`use_bytes=True` may have issues on python2."
"Use `use_bytes='force'` to use it at your own risk.")
if self.options.cache:
if self.options.parser != 'lalr':
raise ConfigurationError("cache only works with parser='lalr' for now")
unhashable = ('transformer', 'postlex', 'lexer_callbacks', 'edit_terminals')
options_str = ''.join(k+str(v) for k, v in options.items() if k not in unhashable)
from . import __version__
s = grammar + options_str + __version__ + str(sys.version_info[:2])
cache_md5 = hashlib.md5(s.encode('utf8')).hexdigest()
if isinstance(self.options.cache, STRING_TYPE):
cache_fn = self.options.cache
else:
if self.options.cache is not True:
raise ConfigurationError("cache argument must be bool or str")
# Python2.7 doesn't support * syntax in tuples
cache_fn = tempfile.gettempdir() + '/.lark_cache_%s_%s_%s.tmp' % ((cache_md5,) + sys.version_info[:2])
if FS.exists(cache_fn):
logger.debug('Loading grammar from cache: %s', cache_fn)
# Remove options that aren't relevant for loading from cache
for name in (set(options) - _LOAD_ALLOWED_OPTIONS):
del options[name]
with FS.open(cache_fn, 'rb') as f:
old_options = self.options
try:
file_md5 = f.readline().rstrip(b'\n')
cached_used_files = pickle.load(f)
if file_md5 == cache_md5.encode('utf8') and verify_used_files(cached_used_files):
cached_parser_data = pickle.load(f)
self._load(cached_parser_data, **options)
return
except Exception: # We should probably narrow done which errors we catch here.
logger.exception("Failed to load Lark from cache: %r. We will try to carry on." % cache_fn)
# In theory, the Lark instance might have been messed up by the call to `_load`.
# In practice the only relevant thing that might have been overriden should be `options`
self.options = old_options
# Parse the grammar file and compose the grammars
self.grammar, used_files = load_grammar(grammar, self.source_path, self.options.import_paths, self.options.keep_all_tokens)
else:
assert isinstance(grammar, Grammar)
self.grammar = grammar
if self.options.lexer == 'auto':
if self.options.parser == 'lalr':
self.options.lexer = 'contextual'
elif self.options.parser == 'earley':
if self.options.postlex is not None:
logger.info("postlex can't be used with the dynamic lexer, so we use standard instead. "
"Consider using lalr with contextual instead of earley")
self.options.lexer = 'standard'
else:
self.options.lexer = 'dynamic'
elif self.options.parser == 'cyk':
self.options.lexer = 'standard'
else:
assert False, self.options.parser
lexer = self.options.lexer
if isinstance(lexer, type):
assert issubclass(lexer, Lexer) # XXX Is this really important? Maybe just ensure interface compliance
else:
assert_config(lexer, ('standard', 'contextual', 'dynamic', 'dynamic_complete'))
if self.options.postlex is not None and 'dynamic' in lexer:
raise ConfigurationError("Can't use postlex with a dynamic lexer. Use standard or contextual instead")
if self.options.ambiguity == 'auto':
if self.options.parser == 'earley':
self.options.ambiguity = 'resolve'
else:
assert_config(self.options.parser, ('earley', 'cyk'), "%r doesn't support disambiguation. Use one of these parsers instead: %s")
if self.options.priority == 'auto':
self.options.priority = 'normal'
if self.options.priority not in _VALID_PRIORITY_OPTIONS:
raise ConfigurationError("invalid priority option: %r. Must be one of %r" % (self.options.priority, _VALID_PRIORITY_OPTIONS))
assert self.options.ambiguity not in ('resolve__antiscore_sum', ), 'resolve__antiscore_sum has been replaced with the option priority="invert"'
if self.options.ambiguity not in _VALID_AMBIGUITY_OPTIONS:
raise ConfigurationError("invalid ambiguity option: %r. Must be one of %r" % (self.options.ambiguity, _VALID_AMBIGUITY_OPTIONS))
if self.options.parser is None:
terminals_to_keep = '*'
elif self.options.postlex is not None:
terminals_to_keep = set(self.options.postlex.always_accept)
else:
terminals_to_keep = set()
# Compile the EBNF grammar into BNF
self.terminals, self.rules, self.ignore_tokens = self.grammar.compile(self.options.start, terminals_to_keep)
if self.options.edit_terminals:
for t in self.terminals:
self.options.edit_terminals(t)
self._terminals_dict = {t.name: t for t in self.terminals}
# If the user asked to invert the priorities, negate them all here.
# This replaces the old 'resolve__antiscore_sum' option.
if self.options.priority == 'invert':
for rule in self.rules:
if rule.options.priority is not None:
rule.options.priority = -rule.options.priority
# Else, if the user asked to disable priorities, strip them from the
# rules. This allows the Earley parsers to skip an extra forest walk
# for improved performance, if you don't need them (or didn't specify any).
elif self.options.priority is None:
for rule in self.rules:
if rule.options.priority is not None:
rule.options.priority = None
# TODO Deprecate lexer_callbacks?
self.lexer_conf = LexerConf(
self.terminals, re_module, self.ignore_tokens, self.options.postlex,
self.options.lexer_callbacks, self.options.g_regex_flags, use_bytes=self.options.use_bytes
)
if self.options.parser:
self.parser = self._build_parser()
elif lexer:
self.lexer = self._build_lexer()
if cache_fn:
logger.debug('Saving grammar to cache: %s', cache_fn)
with FS.open(cache_fn, 'wb') as f:
f.write(cache_md5.encode('utf8') + b'\n')
pickle.dump(used_files, f)
self.save(f)
if __doc__:
__doc__ += "\n\n" + LarkOptions.OPTIONS_DOC
__serialize_fields__ = 'parser', 'rules', 'options'
def _build_lexer(self, dont_ignore=False):
lexer_conf = self.lexer_conf
if dont_ignore:
from copy import copy
lexer_conf = copy(lexer_conf)
lexer_conf.ignore = ()
return TraditionalLexer(lexer_conf)
def _prepare_callbacks(self):
self._callbacks = {}
# we don't need these callbacks if we aren't building a tree
if self.options.ambiguity != 'forest':
self._parse_tree_builder = ParseTreeBuilder(
self.rules,
self.options.tree_class or Tree,
self.options.propagate_positions,
self.options.parser != 'lalr' and self.options.ambiguity == 'explicit',
self.options.maybe_placeholders
)
self._callbacks = self._parse_tree_builder.create_callback(self.options.transformer)
self._callbacks.update(_get_lexer_callbacks(self.options.transformer, self.terminals))
def _build_parser(self):
self._prepare_callbacks()
parser_class = get_frontend(self.options.parser, self.options.lexer)
parser_conf = ParserConf(self.rules, self._callbacks, self.options.start)
return parser_class(self.lexer_conf, parser_conf, options=self.options)
def save(self, f):
"""Saves the instance into the given file object
Useful for caching and multiprocessing.
"""
data, m = self.memo_serialize([TerminalDef, Rule])
pickle.dump({'data': data, 'memo': m}, f, protocol=pickle.HIGHEST_PROTOCOL)
@classmethod
def load(cls, f):
"""Loads an instance from the given file object
Useful for caching and multiprocessing.
"""
inst = cls.__new__(cls)
return inst._load(f)
def _deserialize_lexer_conf(self, data, memo, options):
lexer_conf = LexerConf.deserialize(data['lexer_conf'], memo)
lexer_conf.callbacks = options.lexer_callbacks or {}
lexer_conf.re_module = regex if options.regex else re
lexer_conf.use_bytes = options.use_bytes
lexer_conf.g_regex_flags = options.g_regex_flags
lexer_conf.skip_validation = True
lexer_conf.postlex = options.postlex
return lexer_conf
def _load(self, f, **kwargs):
if isinstance(f, dict):
d = f
else:
d = pickle.load(f)
memo_json = d['memo']
data = d['data']
assert memo_json
memo = SerializeMemoizer.deserialize(memo_json, {'Rule': Rule, 'TerminalDef': TerminalDef}, {})
options = dict(data['options'])
if (set(kwargs) - _LOAD_ALLOWED_OPTIONS) & set(LarkOptions._defaults):
raise ConfigurationError("Some options are not allowed when loading a Parser: {}"
.format(set(kwargs) - _LOAD_ALLOWED_OPTIONS))
options.update(kwargs)
self.options = LarkOptions.deserialize(options, memo)
self.rules = [Rule.deserialize(r, memo) for r in data['rules']]
self.source_path = '<deserialized>'
parser_class = get_frontend(self.options.parser, self.options.lexer)
self.lexer_conf = self._deserialize_lexer_conf(data['parser'], memo, self.options)
self.terminals = self.lexer_conf.terminals
self._prepare_callbacks()
self._terminals_dict = {t.name: t for t in self.terminals}
self.parser = parser_class.deserialize(
data['parser'],
memo,
self.lexer_conf,
self._callbacks,
self.options, # Not all, but multiple attributes are used
)
return self
@classmethod
def _load_from_dict(cls, data, memo, **kwargs):
inst = cls.__new__(cls)
return inst._load({'data': data, 'memo': memo}, **kwargs)
@classmethod
def open(cls, grammar_filename, rel_to=None, **options):
"""Create an instance of Lark with the grammar given by its filename
If ``rel_to`` is provided, the function will find the grammar filename in relation to it.
Example:
>>> Lark.open("grammar_file.lark", rel_to=__file__, parser="lalr")
Lark(...)
"""
if rel_to:
basepath = os.path.dirname(rel_to)
grammar_filename = os.path.join(basepath, grammar_filename)
with open(grammar_filename, encoding='utf8') as f:
return cls(f, **options)
@classmethod
def open_from_package(cls, package, grammar_path, search_paths=("",), **options):
"""Create an instance of Lark with the grammar loaded from within the package `package`.
This allows grammar loading from zipapps.
Imports in the grammar will use the `package` and `search_paths` provided, through `FromPackageLoader`
Example:
Lark.open_from_package(__name__, "example.lark", ("grammars",), parser=...)
"""
package_loader = FromPackageLoader(package, search_paths)
full_path, text = package_loader(None, grammar_path)
options.setdefault('source_path', full_path)
options.setdefault('import_paths', [])
options['import_paths'].append(package_loader)
return cls(text, **options)
def __repr__(self):
return 'Lark(open(%r), parser=%r, lexer=%r, ...)' % (self.source_path, self.options.parser, self.options.lexer)
def lex(self, text, dont_ignore=False):
"""Only lex (and postlex) the text, without parsing it. Only relevant when lexer='standard'
When dont_ignore=True, the lexer will return all tokens, even those marked for %ignore.
:raises UnexpectedCharacters: In case the lexer cannot find a suitable match.
"""
if not hasattr(self, 'lexer') or dont_ignore:
lexer = self._build_lexer(dont_ignore)
else:
lexer = self.lexer
lexer_thread = LexerThread(lexer, text)
stream = lexer_thread.lex(None)
if self.options.postlex:
return self.options.postlex.process(stream)
return stream
def get_terminal(self, name):
"""Get information about a terminal"""
return self._terminals_dict[name]
def parse_interactive(self, text=None, start=None):
"""Start an interactive parsing session.
Parameters:
text (str, optional): Text to be parsed. Required for ``resume_parse()``.
start (str, optional): Start symbol
Returns:
A new InteractiveParser instance.
See Also: ``Lark.parse()``
"""
return self.parser.parse_interactive(text, start=start)
def parse(self, text, start=None, on_error=None):
"""Parse the given text, according to the options provided.
Parameters:
text (str): Text to be parsed.
start (str, optional): Required if Lark was given multiple possible start symbols (using the start option).
on_error (function, optional): if provided, will be called on UnexpectedToken error. Return true to resume parsing.
LALR only. See examples/advanced/error_handling.py for an example of how to use on_error.
Returns:
If a transformer is supplied to ``__init__``, returns whatever is the
result of the transformation. Otherwise, returns a Tree instance.
:raises UnexpectedInput: On a parse error, one of these sub-exceptions will rise:
``UnexpectedCharacters``, ``UnexpectedToken``, or ``UnexpectedEOF``.
For convenience, these sub-exceptions also inherit from ``ParserError`` and ``LexerError``.
"""
return self.parser.parse(text, start=start, on_error=on_error)
@property
def source(self):
warn("Attribute Lark.source was renamed to Lark.source_path", DeprecationWarning)
return self.source_path
@source.setter
def source(self, value):
self.source_path = value
@property
def grammar_source(self):
warn("Attribute Lark.grammar_source was renamed to Lark.source_grammar", DeprecationWarning)
return self.source_grammar
@grammar_source.setter
def grammar_source(self, value):
self.source_grammar = value
###}
