Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.8/site-packages/lark/visitors.py: 70%
270 statements
« prev ^ index » next coverage.py v7.3.1, created at 2023-09-25 06:30 +0000
1from typing import TypeVar, Tuple, List, Callable, Generic, Type, Union, Optional, Any, cast
2from abc import ABC
4from .utils import combine_alternatives
5from .tree import Tree, Branch
6from .exceptions import VisitError, GrammarError
7from .lexer import Token
9###{standalone
10from functools import wraps, update_wrapper
11from inspect import getmembers, getmro
13_Return_T = TypeVar('_Return_T')
14_Return_V = TypeVar('_Return_V')
15_Leaf_T = TypeVar('_Leaf_T')
16_Leaf_U = TypeVar('_Leaf_U')
17_R = TypeVar('_R')
18_FUNC = Callable[..., _Return_T]
19_DECORATED = Union[_FUNC, type]
21class _DiscardType:
22 """When the Discard value is returned from a transformer callback,
23 that node is discarded and won't appear in the parent.
25 Note:
26 This feature is disabled when the transformer is provided to Lark
27 using the ``transformer`` keyword (aka Tree-less LALR mode).
29 Example:
30 ::
32 class T(Transformer):
33 def ignore_tree(self, children):
34 return Discard
36 def IGNORE_TOKEN(self, token):
37 return Discard
38 """
40 def __repr__(self):
41 return "lark.visitors.Discard"
43Discard = _DiscardType()
45# Transformers
47class _Decoratable:
48 "Provides support for decorating methods with @v_args"
50 @classmethod
51 def _apply_v_args(cls, visit_wrapper):
52 mro = getmro(cls)
53 assert mro[0] is cls
54 libmembers = {name for _cls in mro[1:] for name, _ in getmembers(_cls)}
55 for name, value in getmembers(cls):
57 # Make sure the function isn't inherited (unless it's overwritten)
58 if name.startswith('_') or (name in libmembers and name not in cls.__dict__):
59 continue
60 if not callable(value):
61 continue
63 # Skip if v_args already applied (at the function level)
64 if isinstance(cls.__dict__[name], _VArgsWrapper):
65 continue
67 setattr(cls, name, _VArgsWrapper(cls.__dict__[name], visit_wrapper))
68 return cls
70 def __class_getitem__(cls, _):
71 return cls
74class Transformer(_Decoratable, ABC, Generic[_Leaf_T, _Return_T]):
75 """Transformers work bottom-up (or depth-first), starting with visiting the leaves and working
76 their way up until ending at the root of the tree.
78 For each node visited, the transformer will call the appropriate method (callbacks), according to the
79 node's ``data``, and use the returned value to replace the node, thereby creating a new tree structure.
81 Transformers can be used to implement map & reduce patterns. Because nodes are reduced from leaf to root,
82 at any point the callbacks may assume the children have already been transformed (if applicable).
84 If the transformer cannot find a method with the right name, it will instead call ``__default__``, which by
85 default creates a copy of the node.
87 To discard a node, return Discard (``lark.visitors.Discard``).
89 ``Transformer`` can do anything ``Visitor`` can do, but because it reconstructs the tree,
90 it is slightly less efficient.
92 A transformer without methods essentially performs a non-memoized partial deepcopy.
94 All these classes implement the transformer interface:
96 - ``Transformer`` - Recursively transforms the tree. This is the one you probably want.
97 - ``Transformer_InPlace`` - Non-recursive. Changes the tree in-place instead of returning new instances
98 - ``Transformer_InPlaceRecursive`` - Recursive. Changes the tree in-place instead of returning new instances
100 Parameters:
101 visit_tokens (bool, optional): Should the transformer visit tokens in addition to rules.
102 Setting this to ``False`` is slightly faster. Defaults to ``True``.
103 (For processing ignored tokens, use the ``lexer_callbacks`` options)
105 """
106 __visit_tokens__ = True # For backwards compatibility
108 def __init__(self, visit_tokens: bool=True) -> None:
109 self.__visit_tokens__ = visit_tokens
111 def _call_userfunc(self, tree, new_children=None):
112 # Assumes tree is already transformed
113 children = new_children if new_children is not None else tree.children
114 try:
115 f = getattr(self, tree.data)
116 except AttributeError:
117 return self.__default__(tree.data, children, tree.meta)
118 else:
119 try:
120 wrapper = getattr(f, 'visit_wrapper', None)
121 if wrapper is not None:
122 return f.visit_wrapper(f, tree.data, children, tree.meta)
123 else:
124 return f(children)
125 except GrammarError:
126 raise
127 except Exception as e:
128 raise VisitError(tree.data, tree, e)
130 def _call_userfunc_token(self, token):
131 try:
132 f = getattr(self, token.type)
133 except AttributeError:
134 return self.__default_token__(token)
135 else:
136 try:
137 return f(token)
138 except GrammarError:
139 raise
140 except Exception as e:
141 raise VisitError(token.type, token, e)
143 def _transform_children(self, children):
144 for c in children:
145 if isinstance(c, Tree):
146 res = self._transform_tree(c)
147 elif self.__visit_tokens__ and isinstance(c, Token):
148 res = self._call_userfunc_token(c)
149 else:
150 res = c
152 if res is not Discard:
153 yield res
155 def _transform_tree(self, tree):
156 children = list(self._transform_children(tree.children))
157 return self._call_userfunc(tree, children)
159 def transform(self, tree: Tree[_Leaf_T]) -> _Return_T:
160 "Transform the given tree, and return the final result"
161 return self._transform_tree(tree)
163 def __mul__(
164 self: 'Transformer[_Leaf_T, Tree[_Leaf_U]]',
165 other: 'Union[Transformer[_Leaf_U, _Return_V], TransformerChain[_Leaf_U, _Return_V,]]'
166 ) -> 'TransformerChain[_Leaf_T, _Return_V]':
167 """Chain two transformers together, returning a new transformer.
168 """
169 return TransformerChain(self, other)
171 def __default__(self, data, children, meta):
172 """Default function that is called if there is no attribute matching ``data``
174 Can be overridden. Defaults to creating a new copy of the tree node (i.e. ``return Tree(data, children, meta)``)
175 """
176 return Tree(data, children, meta)
178 def __default_token__(self, token):
179 """Default function that is called if there is no attribute matching ``token.type``
181 Can be overridden. Defaults to returning the token as-is.
182 """
183 return token
186def merge_transformers(base_transformer=None, **transformers_to_merge):
187 """Merge a collection of transformers into the base_transformer, each into its own 'namespace'.
189 When called, it will collect the methods from each transformer, and assign them to base_transformer,
190 with their name prefixed with the given keyword, as ``prefix__methodname``.
192 This function is especially useful for processing grammars that import other grammars,
193 thereby creating some of their rules in a 'namespace'. (i.e with a consistent name prefix).
194 In this case, the key for the transformer should match the name of the imported grammar.
196 Parameters:
197 base_transformer (Transformer, optional): The transformer that all other transformers will be added to.
198 **transformers_to_merge: Keyword arguments, in the form of ``name_prefix = transformer``.
200 Raises:
201 AttributeError: In case of a name collision in the merged methods
203 Example:
204 ::
206 class TBase(Transformer):
207 def start(self, children):
208 return children[0] + 'bar'
210 class TImportedGrammar(Transformer):
211 def foo(self, children):
212 return "foo"
214 composed_transformer = merge_transformers(TBase(), imported=TImportedGrammar())
216 t = Tree('start', [ Tree('imported__foo', []) ])
218 assert composed_transformer.transform(t) == 'foobar'
220 """
221 if base_transformer is None:
222 base_transformer = Transformer()
223 for prefix, transformer in transformers_to_merge.items():
224 for method_name in dir(transformer):
225 method = getattr(transformer, method_name)
226 if not callable(method):
227 continue
228 if method_name.startswith("_") or method_name == "transform":
229 continue
230 prefixed_method = prefix + "__" + method_name
231 if hasattr(base_transformer, prefixed_method):
232 raise AttributeError("Cannot merge: method '%s' appears more than once" % prefixed_method)
234 setattr(base_transformer, prefixed_method, method)
236 return base_transformer
239class InlineTransformer(Transformer): # XXX Deprecated
240 def _call_userfunc(self, tree, new_children=None):
241 # Assumes tree is already transformed
242 children = new_children if new_children is not None else tree.children
243 try:
244 f = getattr(self, tree.data)
245 except AttributeError:
246 return self.__default__(tree.data, children, tree.meta)
247 else:
248 return f(*children)
251class TransformerChain(Generic[_Leaf_T, _Return_T]):
253 transformers: 'Tuple[Union[Transformer, TransformerChain], ...]'
255 def __init__(self, *transformers: 'Union[Transformer, TransformerChain]') -> None:
256 self.transformers = transformers
258 def transform(self, tree: Tree[_Leaf_T]) -> _Return_T:
259 for t in self.transformers:
260 tree = t.transform(tree)
261 return cast(_Return_T, tree)
263 def __mul__(
264 self: 'TransformerChain[_Leaf_T, Tree[_Leaf_U]]',
265 other: 'Union[Transformer[_Leaf_U, _Return_V], TransformerChain[_Leaf_U, _Return_V]]'
266 ) -> 'TransformerChain[_Leaf_T, _Return_V]':
267 return TransformerChain(*self.transformers + (other,))
270class Transformer_InPlace(Transformer):
271 """Same as Transformer, but non-recursive, and changes the tree in-place instead of returning new instances
273 Useful for huge trees. Conservative in memory.
274 """
275 def _transform_tree(self, tree): # Cancel recursion
276 return self._call_userfunc(tree)
278 def transform(self, tree: Tree[_Leaf_T]) -> _Return_T:
279 for subtree in tree.iter_subtrees():
280 subtree.children = list(self._transform_children(subtree.children))
282 return self._transform_tree(tree)
285class Transformer_NonRecursive(Transformer):
286 """Same as Transformer but non-recursive.
288 Like Transformer, it doesn't change the original tree.
290 Useful for huge trees.
291 """
293 def transform(self, tree: Tree[_Leaf_T]) -> _Return_T:
294 # Tree to postfix
295 rev_postfix = []
296 q: List[Branch[_Leaf_T]] = [tree]
297 while q:
298 t = q.pop()
299 rev_postfix.append(t)
300 if isinstance(t, Tree):
301 q += t.children
303 # Postfix to tree
304 stack: List = []
305 for x in reversed(rev_postfix):
306 if isinstance(x, Tree):
307 size = len(x.children)
308 if size:
309 args = stack[-size:]
310 del stack[-size:]
311 else:
312 args = []
314 res = self._call_userfunc(x, args)
315 if res is not Discard:
316 stack.append(res)
318 elif self.__visit_tokens__ and isinstance(x, Token):
319 res = self._call_userfunc_token(x)
320 if res is not Discard:
321 stack.append(res)
322 else:
323 stack.append(x)
325 result, = stack # We should have only one tree remaining
326 # There are no guarantees on the type of the value produced by calling a user func for a
327 # child will produce. This means type system can't statically know that the final result is
328 # _Return_T. As a result a cast is required.
329 return cast(_Return_T, result)
332class Transformer_InPlaceRecursive(Transformer):
333 "Same as Transformer, recursive, but changes the tree in-place instead of returning new instances"
334 def _transform_tree(self, tree):
335 tree.children = list(self._transform_children(tree.children))
336 return self._call_userfunc(tree)
339# Visitors
341class VisitorBase:
342 def _call_userfunc(self, tree):
343 return getattr(self, tree.data, self.__default__)(tree)
345 def __default__(self, tree):
346 """Default function that is called if there is no attribute matching ``tree.data``
348 Can be overridden. Defaults to doing nothing.
349 """
350 return tree
352 def __class_getitem__(cls, _):
353 return cls
356class Visitor(VisitorBase, ABC, Generic[_Leaf_T]):
357 """Tree visitor, non-recursive (can handle huge trees).
359 Visiting a node calls its methods (provided by the user via inheritance) according to ``tree.data``
360 """
362 def visit(self, tree: Tree[_Leaf_T]) -> Tree[_Leaf_T]:
363 "Visits the tree, starting with the leaves and finally the root (bottom-up)"
364 for subtree in tree.iter_subtrees():
365 self._call_userfunc(subtree)
366 return tree
368 def visit_topdown(self, tree: Tree[_Leaf_T]) -> Tree[_Leaf_T]:
369 "Visit the tree, starting at the root, and ending at the leaves (top-down)"
370 for subtree in tree.iter_subtrees_topdown():
371 self._call_userfunc(subtree)
372 return tree
375class Visitor_Recursive(VisitorBase, Generic[_Leaf_T]):
376 """Bottom-up visitor, recursive.
378 Visiting a node calls its methods (provided by the user via inheritance) according to ``tree.data``
380 Slightly faster than the non-recursive version.
381 """
383 def visit(self, tree: Tree[_Leaf_T]) -> Tree[_Leaf_T]:
384 "Visits the tree, starting with the leaves and finally the root (bottom-up)"
385 for child in tree.children:
386 if isinstance(child, Tree):
387 self.visit(child)
389 self._call_userfunc(tree)
390 return tree
392 def visit_topdown(self,tree: Tree[_Leaf_T]) -> Tree[_Leaf_T]:
393 "Visit the tree, starting at the root, and ending at the leaves (top-down)"
394 self._call_userfunc(tree)
396 for child in tree.children:
397 if isinstance(child, Tree):
398 self.visit_topdown(child)
400 return tree
403class Interpreter(_Decoratable, ABC, Generic[_Leaf_T, _Return_T]):
404 """Interpreter walks the tree starting at the root.
406 Visits the tree, starting with the root and finally the leaves (top-down)
408 For each tree node, it calls its methods (provided by user via inheritance) according to ``tree.data``.
410 Unlike ``Transformer`` and ``Visitor``, the Interpreter doesn't automatically visit its sub-branches.
411 The user has to explicitly call ``visit``, ``visit_children``, or use the ``@visit_children_decor``.
412 This allows the user to implement branching and loops.
413 """
415 def visit(self, tree: Tree[_Leaf_T]) -> _Return_T:
416 # There are no guarantees on the type of the value produced by calling a user func for a
417 # child will produce. So only annotate the public method and use an internal method when
418 # visiting child trees.
419 return self._visit_tree(tree)
421 def _visit_tree(self, tree: Tree[_Leaf_T]):
422 f = getattr(self, tree.data)
423 wrapper = getattr(f, 'visit_wrapper', None)
424 if wrapper is not None:
425 return f.visit_wrapper(f, tree.data, tree.children, tree.meta)
426 else:
427 return f(tree)
429 def visit_children(self, tree: Tree[_Leaf_T]) -> List:
430 return [self._visit_tree(child) if isinstance(child, Tree) else child
431 for child in tree.children]
433 def __getattr__(self, name):
434 return self.__default__
436 def __default__(self, tree):
437 return self.visit_children(tree)
440_InterMethod = Callable[[Type[Interpreter], _Return_T], _R]
442def visit_children_decor(func: _InterMethod) -> _InterMethod:
443 "See Interpreter"
444 @wraps(func)
445 def inner(cls, tree):
446 values = cls.visit_children(tree)
447 return func(cls, values)
448 return inner
450# Decorators
452def _apply_v_args(obj, visit_wrapper):
453 try:
454 _apply = obj._apply_v_args
455 except AttributeError:
456 return _VArgsWrapper(obj, visit_wrapper)
457 else:
458 return _apply(visit_wrapper)
461class _VArgsWrapper:
462 """
463 A wrapper around a Callable. It delegates `__call__` to the Callable.
464 If the Callable has a `__get__`, that is also delegate and the resulting function is wrapped.
465 Otherwise, we use the original function mirroring the behaviour without a __get__.
466 We also have the visit_wrapper attribute to be used by Transformers.
467 """
468 base_func: Callable
470 def __init__(self, func: Callable, visit_wrapper: Callable[[Callable, str, list, Any], Any]):
471 if isinstance(func, _VArgsWrapper):
472 func = func.base_func
473 # https://github.com/python/mypy/issues/708
474 self.base_func = func # type: ignore[assignment]
475 self.visit_wrapper = visit_wrapper
476 update_wrapper(self, func)
478 def __call__(self, *args, **kwargs):
479 return self.base_func(*args, **kwargs)
481 def __get__(self, instance, owner=None):
482 try:
483 # Use the __get__ attribute of the type instead of the instance
484 # to fully mirror the behavior of getattr
485 g = type(self.base_func).__get__
486 except AttributeError:
487 return self
488 else:
489 return _VArgsWrapper(g(self.base_func, instance, owner), self.visit_wrapper)
491 def __set_name__(self, owner, name):
492 try:
493 f = type(self.base_func).__set_name__
494 except AttributeError:
495 return
496 else:
497 f(self.base_func, owner, name)
500def _vargs_inline(f, _data, children, _meta):
501 return f(*children)
502def _vargs_meta_inline(f, _data, children, meta):
503 return f(meta, *children)
504def _vargs_meta(f, _data, children, meta):
505 return f(meta, children)
506def _vargs_tree(f, data, children, meta):
507 return f(Tree(data, children, meta))
510def v_args(inline: bool = False, meta: bool = False, tree: bool = False, wrapper: Optional[Callable] = None) -> Callable[[_DECORATED], _DECORATED]:
511 """A convenience decorator factory for modifying the behavior of user-supplied visitor methods.
513 By default, callback methods of transformers/visitors accept one argument - a list of the node's children.
515 ``v_args`` can modify this behavior. When used on a transformer/visitor class definition,
516 it applies to all the callback methods inside it.
518 ``v_args`` can be applied to a single method, or to an entire class. When applied to both,
519 the options given to the method take precedence.
521 Parameters:
522 inline (bool, optional): Children are provided as ``*args`` instead of a list argument (not recommended for very long lists).
523 meta (bool, optional): Provides two arguments: ``meta`` and ``children`` (instead of just the latter)
524 tree (bool, optional): Provides the entire tree as the argument, instead of the children.
525 wrapper (function, optional): Provide a function to decorate all methods.
527 Example:
528 ::
530 @v_args(inline=True)
531 class SolveArith(Transformer):
532 def add(self, left, right):
533 return left + right
535 @v_args(meta=True)
536 def mul(self, meta, children):
537 logger.info(f'mul at line {meta.line}')
538 left, right = children
539 return left * right
542 class ReverseNotation(Transformer_InPlace):
543 @v_args(tree=True)
544 def tree_node(self, tree):
545 tree.children = tree.children[::-1]
546 """
547 if tree and (meta or inline):
548 raise ValueError("Visitor functions cannot combine 'tree' with 'meta' or 'inline'.")
550 func = None
551 if meta:
552 if inline:
553 func = _vargs_meta_inline
554 else:
555 func = _vargs_meta
556 elif inline:
557 func = _vargs_inline
558 elif tree:
559 func = _vargs_tree
561 if wrapper is not None:
562 if func is not None:
563 raise ValueError("Cannot use 'wrapper' along with 'tree', 'meta' or 'inline'.")
564 func = wrapper
566 def _visitor_args_dec(obj):
567 return _apply_v_args(obj, func)
568 return _visitor_args_dec
571###}
574# --- Visitor Utilities ---
576class CollapseAmbiguities(Transformer):
577 """
578 Transforms a tree that contains any number of _ambig nodes into a list of trees,
579 each one containing an unambiguous tree.
581 The length of the resulting list is the product of the length of all _ambig nodes.
583 Warning: This may quickly explode for highly ambiguous trees.
585 """
586 def _ambig(self, options):
587 return sum(options, [])
589 def __default__(self, data, children_lists, meta):
590 return [Tree(data, children, meta) for children in combine_alternatives(children_lists)]
592 def __default_token__(self, t):
593 return [t]