1476 lines
53 KiB
Python
1476 lines
53 KiB
Python
# Natural Language Toolkit: Regular Expression Chunkers
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#
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# Copyright (C) 2001-2023 NLTK Project
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# Author: Edward Loper <edloper@gmail.com>
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# Steven Bird <stevenbird1@gmail.com> (minor additions)
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# URL: <https://www.nltk.org/>
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# For license information, see LICENSE.TXT
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import re
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import regex
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from nltk.chunk.api import ChunkParserI
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from nltk.tree import Tree
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# //////////////////////////////////////////////////////
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# ChunkString
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# //////////////////////////////////////////////////////
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class ChunkString:
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"""
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A string-based encoding of a particular chunking of a text.
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Internally, the ``ChunkString`` class uses a single string to
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encode the chunking of the input text. This string contains a
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sequence of angle-bracket delimited tags, with chunking indicated
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by braces. An example of this encoding is::
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{<DT><JJ><NN>}<VBN><IN>{<DT><NN>}<.>{<DT><NN>}<VBD><.>
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``ChunkString`` are created from tagged texts (i.e., lists of
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``tokens`` whose type is ``TaggedType``). Initially, nothing is
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chunked.
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The chunking of a ``ChunkString`` can be modified with the ``xform()``
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method, which uses a regular expression to transform the string
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representation. These transformations should only add and remove
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braces; they should *not* modify the sequence of angle-bracket
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delimited tags.
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:type _str: str
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:ivar _str: The internal string representation of the text's
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encoding. This string representation contains a sequence of
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angle-bracket delimited tags, with chunking indicated by
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braces. An example of this encoding is::
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{<DT><JJ><NN>}<VBN><IN>{<DT><NN>}<.>{<DT><NN>}<VBD><.>
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:type _pieces: list(tagged tokens and chunks)
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:ivar _pieces: The tagged tokens and chunks encoded by this ``ChunkString``.
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:ivar _debug: The debug level. See the constructor docs.
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:cvar IN_CHUNK_PATTERN: A zero-width regexp pattern string that
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will only match positions that are in chunks.
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:cvar IN_STRIP_PATTERN: A zero-width regexp pattern string that
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will only match positions that are in strips.
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"""
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CHUNK_TAG_CHAR = r"[^\{\}<>]"
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CHUNK_TAG = r"(<%s+?>)" % CHUNK_TAG_CHAR
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IN_CHUNK_PATTERN = r"(?=[^\{]*\})"
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IN_STRIP_PATTERN = r"(?=[^\}]*(\{|$))"
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# These are used by _verify
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_CHUNK = r"(\{%s+?\})+?" % CHUNK_TAG
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_STRIP = r"(%s+?)+?" % CHUNK_TAG
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_VALID = re.compile(r"^(\{?%s\}?)*?$" % CHUNK_TAG)
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_BRACKETS = re.compile(r"[^\{\}]+")
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_BALANCED_BRACKETS = re.compile(r"(\{\})*$")
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def __init__(self, chunk_struct, debug_level=1):
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"""
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Construct a new ``ChunkString`` that encodes the chunking of
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the text ``tagged_tokens``.
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:type chunk_struct: Tree
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:param chunk_struct: The chunk structure to be further chunked.
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:type debug_level: int
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:param debug_level: The level of debugging which should be
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applied to transformations on the ``ChunkString``. The
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valid levels are:
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- 0: no checks
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- 1: full check on to_chunkstruct
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- 2: full check on to_chunkstruct and cursory check after
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each transformation.
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- 3: full check on to_chunkstruct and full check after
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each transformation.
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We recommend you use at least level 1. You should
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probably use level 3 if you use any non-standard
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subclasses of ``RegexpChunkRule``.
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"""
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self._root_label = chunk_struct.label()
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self._pieces = chunk_struct[:]
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tags = [self._tag(tok) for tok in self._pieces]
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self._str = "<" + "><".join(tags) + ">"
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self._debug = debug_level
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def _tag(self, tok):
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if isinstance(tok, tuple):
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return tok[1]
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elif isinstance(tok, Tree):
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return tok.label()
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else:
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raise ValueError("chunk structures must contain tagged " "tokens or trees")
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def _verify(self, s, verify_tags):
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"""
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Check to make sure that ``s`` still corresponds to some chunked
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version of ``_pieces``.
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:type verify_tags: bool
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:param verify_tags: Whether the individual tags should be
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checked. If this is false, ``_verify`` will check to make
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sure that ``_str`` encodes a chunked version of *some*
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list of tokens. If this is true, then ``_verify`` will
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check to make sure that the tags in ``_str`` match those in
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``_pieces``.
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:raise ValueError: if the internal string representation of
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this ``ChunkString`` is invalid or not consistent with _pieces.
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"""
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# Check overall form
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if not ChunkString._VALID.match(s):
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raise ValueError(
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"Transformation generated invalid " "chunkstring:\n %s" % s
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)
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# Check that parens are balanced. If the string is long, we
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# have to do this in pieces, to avoid a maximum recursion
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# depth limit for regular expressions.
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brackets = ChunkString._BRACKETS.sub("", s)
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for i in range(1 + len(brackets) // 5000):
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substr = brackets[i * 5000 : i * 5000 + 5000]
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if not ChunkString._BALANCED_BRACKETS.match(substr):
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raise ValueError(
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"Transformation generated invalid " "chunkstring:\n %s" % s
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)
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if verify_tags <= 0:
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return
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tags1 = (re.split(r"[\{\}<>]+", s))[1:-1]
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tags2 = [self._tag(piece) for piece in self._pieces]
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if tags1 != tags2:
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raise ValueError(
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"Transformation generated invalid " "chunkstring: tag changed"
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)
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def to_chunkstruct(self, chunk_label="CHUNK"):
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"""
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Return the chunk structure encoded by this ``ChunkString``.
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:rtype: Tree
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:raise ValueError: If a transformation has generated an
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invalid chunkstring.
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"""
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if self._debug > 0:
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self._verify(self._str, 1)
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# Use this alternating list to create the chunkstruct.
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pieces = []
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index = 0
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piece_in_chunk = 0
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for piece in re.split("[{}]", self._str):
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# Find the list of tokens contained in this piece.
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length = piece.count("<")
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subsequence = self._pieces[index : index + length]
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# Add this list of tokens to our pieces.
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if piece_in_chunk:
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pieces.append(Tree(chunk_label, subsequence))
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else:
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pieces += subsequence
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# Update index, piece_in_chunk
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index += length
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piece_in_chunk = not piece_in_chunk
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return Tree(self._root_label, pieces)
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def xform(self, regexp, repl):
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"""
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Apply the given transformation to the string encoding of this
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``ChunkString``. In particular, find all occurrences that match
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``regexp``, and replace them using ``repl`` (as done by
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``re.sub``).
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This transformation should only add and remove braces; it
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should *not* modify the sequence of angle-bracket delimited
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tags. Furthermore, this transformation may not result in
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improper bracketing. Note, in particular, that bracketing may
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not be nested.
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:type regexp: str or regexp
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:param regexp: A regular expression matching the substring
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that should be replaced. This will typically include a
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named group, which can be used by ``repl``.
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:type repl: str
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:param repl: An expression specifying what should replace the
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matched substring. Typically, this will include a named
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replacement group, specified by ``regexp``.
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:rtype: None
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:raise ValueError: If this transformation generated an
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invalid chunkstring.
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"""
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# Do the actual substitution
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s = re.sub(regexp, repl, self._str)
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# The substitution might have generated "empty chunks"
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# (substrings of the form "{}"). Remove them, so they don't
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# interfere with other transformations.
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s = re.sub(r"\{\}", "", s)
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# Make sure that the transformation was legal.
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if self._debug > 1:
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self._verify(s, self._debug - 2)
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# Commit the transformation.
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self._str = s
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def __repr__(self):
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"""
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Return a string representation of this ``ChunkString``.
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It has the form::
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<ChunkString: '{<DT><JJ><NN>}<VBN><IN>{<DT><NN>}'>
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:rtype: str
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"""
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return "<ChunkString: %s>" % repr(self._str)
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def __str__(self):
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"""
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Return a formatted representation of this ``ChunkString``.
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This representation will include extra spaces to ensure that
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tags will line up with the representation of other
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``ChunkStrings`` for the same text, regardless of the chunking.
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:rtype: str
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"""
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# Add spaces to make everything line up.
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str = re.sub(r">(?!\})", r"> ", self._str)
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str = re.sub(r"([^\{])<", r"\1 <", str)
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if str[0] == "<":
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str = " " + str
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return str
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# //////////////////////////////////////////////////////
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# Chunking Rules
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# //////////////////////////////////////////////////////
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class RegexpChunkRule:
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"""
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A rule specifying how to modify the chunking in a ``ChunkString``,
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using a transformational regular expression. The
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``RegexpChunkRule`` class itself can be used to implement any
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transformational rule based on regular expressions. There are
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also a number of subclasses, which can be used to implement
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simpler types of rules, based on matching regular expressions.
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Each ``RegexpChunkRule`` has a regular expression and a
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replacement expression. When a ``RegexpChunkRule`` is "applied"
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to a ``ChunkString``, it searches the ``ChunkString`` for any
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substring that matches the regular expression, and replaces it
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using the replacement expression. This search/replace operation
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has the same semantics as ``re.sub``.
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Each ``RegexpChunkRule`` also has a description string, which
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gives a short (typically less than 75 characters) description of
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the purpose of the rule.
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This transformation defined by this ``RegexpChunkRule`` should
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only add and remove braces; it should *not* modify the sequence
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of angle-bracket delimited tags. Furthermore, this transformation
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may not result in nested or mismatched bracketing.
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"""
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def __init__(self, regexp, repl, descr):
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"""
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Construct a new RegexpChunkRule.
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:type regexp: regexp or str
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:param regexp: The regular expression for this ``RegexpChunkRule``.
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When this rule is applied to a ``ChunkString``, any
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substring that matches ``regexp`` will be replaced using
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the replacement string ``repl``. Note that this must be a
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normal regular expression, not a tag pattern.
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:type repl: str
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:param repl: The replacement expression for this ``RegexpChunkRule``.
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When this rule is applied to a ``ChunkString``, any substring
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that matches ``regexp`` will be replaced using ``repl``.
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:type descr: str
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:param descr: A short description of the purpose and/or effect
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of this rule.
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"""
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if isinstance(regexp, str):
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regexp = re.compile(regexp)
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self._repl = repl
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self._descr = descr
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self._regexp = regexp
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def apply(self, chunkstr):
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# Keep docstring generic so we can inherit it.
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"""
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Apply this rule to the given ``ChunkString``. See the
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class reference documentation for a description of what it
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means to apply a rule.
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:type chunkstr: ChunkString
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:param chunkstr: The chunkstring to which this rule is applied.
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:rtype: None
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:raise ValueError: If this transformation generated an
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invalid chunkstring.
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"""
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chunkstr.xform(self._regexp, self._repl)
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def descr(self):
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"""
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Return a short description of the purpose and/or effect of
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this rule.
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:rtype: str
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"""
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return self._descr
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def __repr__(self):
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"""
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Return a string representation of this rule. It has the form::
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<RegexpChunkRule: '{<IN|VB.*>}'->'<IN>'>
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Note that this representation does not include the
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description string; that string can be accessed
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separately with the ``descr()`` method.
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:rtype: str
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"""
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return (
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"<RegexpChunkRule: "
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+ repr(self._regexp.pattern)
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+ "->"
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+ repr(self._repl)
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+ ">"
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)
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@staticmethod
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def fromstring(s):
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"""
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Create a RegexpChunkRule from a string description.
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Currently, the following formats are supported::
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{regexp} # chunk rule
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}regexp{ # strip rule
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regexp}{regexp # split rule
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regexp{}regexp # merge rule
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Where ``regexp`` is a regular expression for the rule. Any
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text following the comment marker (``#``) will be used as
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the rule's description:
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>>> from nltk.chunk.regexp import RegexpChunkRule
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>>> RegexpChunkRule.fromstring('{<DT>?<NN.*>+}')
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<ChunkRule: '<DT>?<NN.*>+'>
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"""
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# Split off the comment (but don't split on '\#')
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m = re.match(r"(?P<rule>(\\.|[^#])*)(?P<comment>#.*)?", s)
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rule = m.group("rule").strip()
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comment = (m.group("comment") or "")[1:].strip()
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# Pattern bodies: chunk, strip, split, merge
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try:
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if not rule:
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raise ValueError("Empty chunk pattern")
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if rule[0] == "{" and rule[-1] == "}":
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return ChunkRule(rule[1:-1], comment)
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elif rule[0] == "}" and rule[-1] == "{":
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return StripRule(rule[1:-1], comment)
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elif "}{" in rule:
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left, right = rule.split("}{")
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return SplitRule(left, right, comment)
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elif "{}" in rule:
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left, right = rule.split("{}")
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return MergeRule(left, right, comment)
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elif re.match("[^{}]*{[^{}]*}[^{}]*", rule):
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left, chunk, right = re.split("[{}]", rule)
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return ChunkRuleWithContext(left, chunk, right, comment)
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else:
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raise ValueError("Illegal chunk pattern: %s" % rule)
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except (ValueError, re.error) as e:
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raise ValueError("Illegal chunk pattern: %s" % rule) from e
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class ChunkRule(RegexpChunkRule):
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"""
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A rule specifying how to add chunks to a ``ChunkString``, using a
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matching tag pattern. When applied to a ``ChunkString``, it will
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find any substring that matches this tag pattern and that is not
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already part of a chunk, and create a new chunk containing that
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substring.
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"""
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def __init__(self, tag_pattern, descr):
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"""
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Construct a new ``ChunkRule``.
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:type tag_pattern: str
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:param tag_pattern: This rule's tag pattern. When
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applied to a ``ChunkString``, this rule will
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chunk any substring that matches this tag pattern and that
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is not already part of a chunk.
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:type descr: str
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:param descr: A short description of the purpose and/or effect
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of this rule.
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"""
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self._pattern = tag_pattern
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regexp = re.compile(
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"(?P<chunk>%s)%s"
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% (tag_pattern2re_pattern(tag_pattern), ChunkString.IN_STRIP_PATTERN)
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)
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RegexpChunkRule.__init__(self, regexp, r"{\g<chunk>}", descr)
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def __repr__(self):
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"""
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Return a string representation of this rule. It has the form::
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<ChunkRule: '<IN|VB.*>'>
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Note that this representation does not include the
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description string; that string can be accessed
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separately with the ``descr()`` method.
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:rtype: str
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"""
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return "<ChunkRule: " + repr(self._pattern) + ">"
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|
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class StripRule(RegexpChunkRule):
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"""
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A rule specifying how to remove strips to a ``ChunkString``,
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using a matching tag pattern. When applied to a
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``ChunkString``, it will find any substring that matches this
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tag pattern and that is contained in a chunk, and remove it
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from that chunk, thus creating two new chunks.
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"""
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def __init__(self, tag_pattern, descr):
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"""
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Construct a new ``StripRule``.
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:type tag_pattern: str
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:param tag_pattern: This rule's tag pattern. When
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applied to a ``ChunkString``, this rule will
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find any substring that matches this tag pattern and that
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is contained in a chunk, and remove it from that chunk,
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thus creating two new chunks.
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:type descr: str
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:param descr: A short description of the purpose and/or effect
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of this rule.
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"""
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self._pattern = tag_pattern
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regexp = re.compile(
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"(?P<strip>%s)%s"
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% (tag_pattern2re_pattern(tag_pattern), ChunkString.IN_CHUNK_PATTERN)
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)
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RegexpChunkRule.__init__(self, regexp, r"}\g<strip>{", descr)
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def __repr__(self):
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"""
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Return a string representation of this rule. It has the form::
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<StripRule: '<IN|VB.*>'>
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Note that this representation does not include the
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description string; that string can be accessed
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separately with the ``descr()`` method.
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:rtype: str
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"""
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return "<StripRule: " + repr(self._pattern) + ">"
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|
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class UnChunkRule(RegexpChunkRule):
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"""
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A rule specifying how to remove chunks to a ``ChunkString``,
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using a matching tag pattern. When applied to a
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``ChunkString``, it will find any complete chunk that matches this
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tag pattern, and un-chunk it.
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"""
|
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def __init__(self, tag_pattern, descr):
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"""
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Construct a new ``UnChunkRule``.
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:type tag_pattern: str
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:param tag_pattern: This rule's tag pattern. When
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applied to a ``ChunkString``, this rule will
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find any complete chunk that matches this tag pattern,
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and un-chunk it.
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:type descr: str
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:param descr: A short description of the purpose and/or effect
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of this rule.
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"""
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self._pattern = tag_pattern
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regexp = re.compile(r"\{(?P<chunk>%s)\}" % tag_pattern2re_pattern(tag_pattern))
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RegexpChunkRule.__init__(self, regexp, r"\g<chunk>", descr)
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|
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def __repr__(self):
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"""
|
|
Return a string representation of this rule. It has the form::
|
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|
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<UnChunkRule: '<IN|VB.*>'>
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|
|
Note that this representation does not include the
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description string; that string can be accessed
|
|
separately with the ``descr()`` method.
|
|
|
|
:rtype: str
|
|
"""
|
|
return "<UnChunkRule: " + repr(self._pattern) + ">"
|
|
|
|
|
|
class MergeRule(RegexpChunkRule):
|
|
"""
|
|
A rule specifying how to merge chunks in a ``ChunkString``, using
|
|
two matching tag patterns: a left pattern, and a right pattern.
|
|
When applied to a ``ChunkString``, it will find any chunk whose end
|
|
matches left pattern, and immediately followed by a chunk whose
|
|
beginning matches right pattern. It will then merge those two
|
|
chunks into a single chunk.
|
|
"""
|
|
|
|
def __init__(self, left_tag_pattern, right_tag_pattern, descr):
|
|
"""
|
|
Construct a new ``MergeRule``.
|
|
|
|
:type right_tag_pattern: str
|
|
:param right_tag_pattern: This rule's right tag
|
|
pattern. When applied to a ``ChunkString``, this
|
|
rule will find any chunk whose end matches
|
|
``left_tag_pattern``, and immediately followed by a chunk
|
|
whose beginning matches this pattern. It will
|
|
then merge those two chunks into a single chunk.
|
|
:type left_tag_pattern: str
|
|
:param left_tag_pattern: This rule's left tag
|
|
pattern. When applied to a ``ChunkString``, this
|
|
rule will find any chunk whose end matches
|
|
this pattern, and immediately followed by a chunk
|
|
whose beginning matches ``right_tag_pattern``. It will
|
|
then merge those two chunks into a single chunk.
|
|
|
|
:type descr: str
|
|
:param descr: A short description of the purpose and/or effect
|
|
of this rule.
|
|
"""
|
|
# Ensure that the individual patterns are coherent. E.g., if
|
|
# left='(' and right=')', then this will raise an exception:
|
|
re.compile(tag_pattern2re_pattern(left_tag_pattern))
|
|
re.compile(tag_pattern2re_pattern(right_tag_pattern))
|
|
|
|
self._left_tag_pattern = left_tag_pattern
|
|
self._right_tag_pattern = right_tag_pattern
|
|
regexp = re.compile(
|
|
"(?P<left>%s)}{(?=%s)"
|
|
% (
|
|
tag_pattern2re_pattern(left_tag_pattern),
|
|
tag_pattern2re_pattern(right_tag_pattern),
|
|
)
|
|
)
|
|
RegexpChunkRule.__init__(self, regexp, r"\g<left>", descr)
|
|
|
|
def __repr__(self):
|
|
"""
|
|
Return a string representation of this rule. It has the form::
|
|
|
|
<MergeRule: '<NN|DT|JJ>', '<NN|JJ>'>
|
|
|
|
Note that this representation does not include the
|
|
description string; that string can be accessed
|
|
separately with the ``descr()`` method.
|
|
|
|
:rtype: str
|
|
"""
|
|
return (
|
|
"<MergeRule: "
|
|
+ repr(self._left_tag_pattern)
|
|
+ ", "
|
|
+ repr(self._right_tag_pattern)
|
|
+ ">"
|
|
)
|
|
|
|
|
|
class SplitRule(RegexpChunkRule):
|
|
"""
|
|
A rule specifying how to split chunks in a ``ChunkString``, using
|
|
two matching tag patterns: a left pattern, and a right pattern.
|
|
When applied to a ``ChunkString``, it will find any chunk that
|
|
matches the left pattern followed by the right pattern. It will
|
|
then split the chunk into two new chunks, at the point between the
|
|
two pattern matches.
|
|
"""
|
|
|
|
def __init__(self, left_tag_pattern, right_tag_pattern, descr):
|
|
"""
|
|
Construct a new ``SplitRule``.
|
|
|
|
:type right_tag_pattern: str
|
|
:param right_tag_pattern: This rule's right tag
|
|
pattern. When applied to a ``ChunkString``, this rule will
|
|
find any chunk containing a substring that matches
|
|
``left_tag_pattern`` followed by this pattern. It will
|
|
then split the chunk into two new chunks at the point
|
|
between these two matching patterns.
|
|
:type left_tag_pattern: str
|
|
:param left_tag_pattern: This rule's left tag
|
|
pattern. When applied to a ``ChunkString``, this rule will
|
|
find any chunk containing a substring that matches this
|
|
pattern followed by ``right_tag_pattern``. It will then
|
|
split the chunk into two new chunks at the point between
|
|
these two matching patterns.
|
|
:type descr: str
|
|
:param descr: A short description of the purpose and/or effect
|
|
of this rule.
|
|
"""
|
|
# Ensure that the individual patterns are coherent. E.g., if
|
|
# left='(' and right=')', then this will raise an exception:
|
|
re.compile(tag_pattern2re_pattern(left_tag_pattern))
|
|
re.compile(tag_pattern2re_pattern(right_tag_pattern))
|
|
|
|
self._left_tag_pattern = left_tag_pattern
|
|
self._right_tag_pattern = right_tag_pattern
|
|
regexp = re.compile(
|
|
"(?P<left>%s)(?=%s)"
|
|
% (
|
|
tag_pattern2re_pattern(left_tag_pattern),
|
|
tag_pattern2re_pattern(right_tag_pattern),
|
|
)
|
|
)
|
|
RegexpChunkRule.__init__(self, regexp, r"\g<left>}{", descr)
|
|
|
|
def __repr__(self):
|
|
"""
|
|
Return a string representation of this rule. It has the form::
|
|
|
|
<SplitRule: '<NN>', '<DT>'>
|
|
|
|
Note that this representation does not include the
|
|
description string; that string can be accessed
|
|
separately with the ``descr()`` method.
|
|
|
|
:rtype: str
|
|
"""
|
|
return (
|
|
"<SplitRule: "
|
|
+ repr(self._left_tag_pattern)
|
|
+ ", "
|
|
+ repr(self._right_tag_pattern)
|
|
+ ">"
|
|
)
|
|
|
|
|
|
class ExpandLeftRule(RegexpChunkRule):
|
|
"""
|
|
A rule specifying how to expand chunks in a ``ChunkString`` to the left,
|
|
using two matching tag patterns: a left pattern, and a right pattern.
|
|
When applied to a ``ChunkString``, it will find any chunk whose beginning
|
|
matches right pattern, and immediately preceded by a strip whose
|
|
end matches left pattern. It will then expand the chunk to incorporate
|
|
the new material on the left.
|
|
"""
|
|
|
|
def __init__(self, left_tag_pattern, right_tag_pattern, descr):
|
|
"""
|
|
Construct a new ``ExpandRightRule``.
|
|
|
|
:type right_tag_pattern: str
|
|
:param right_tag_pattern: This rule's right tag
|
|
pattern. When applied to a ``ChunkString``, this
|
|
rule will find any chunk whose beginning matches
|
|
``right_tag_pattern``, and immediately preceded by a strip
|
|
whose end matches this pattern. It will
|
|
then merge those two chunks into a single chunk.
|
|
:type left_tag_pattern: str
|
|
:param left_tag_pattern: This rule's left tag
|
|
pattern. When applied to a ``ChunkString``, this
|
|
rule will find any chunk whose beginning matches
|
|
this pattern, and immediately preceded by a strip
|
|
whose end matches ``left_tag_pattern``. It will
|
|
then expand the chunk to incorporate the new material on the left.
|
|
|
|
:type descr: str
|
|
:param descr: A short description of the purpose and/or effect
|
|
of this rule.
|
|
"""
|
|
# Ensure that the individual patterns are coherent. E.g., if
|
|
# left='(' and right=')', then this will raise an exception:
|
|
re.compile(tag_pattern2re_pattern(left_tag_pattern))
|
|
re.compile(tag_pattern2re_pattern(right_tag_pattern))
|
|
|
|
self._left_tag_pattern = left_tag_pattern
|
|
self._right_tag_pattern = right_tag_pattern
|
|
regexp = re.compile(
|
|
r"(?P<left>%s)\{(?P<right>%s)"
|
|
% (
|
|
tag_pattern2re_pattern(left_tag_pattern),
|
|
tag_pattern2re_pattern(right_tag_pattern),
|
|
)
|
|
)
|
|
RegexpChunkRule.__init__(self, regexp, r"{\g<left>\g<right>", descr)
|
|
|
|
def __repr__(self):
|
|
"""
|
|
Return a string representation of this rule. It has the form::
|
|
|
|
<ExpandLeftRule: '<NN|DT|JJ>', '<NN|JJ>'>
|
|
|
|
Note that this representation does not include the
|
|
description string; that string can be accessed
|
|
separately with the ``descr()`` method.
|
|
|
|
:rtype: str
|
|
"""
|
|
return (
|
|
"<ExpandLeftRule: "
|
|
+ repr(self._left_tag_pattern)
|
|
+ ", "
|
|
+ repr(self._right_tag_pattern)
|
|
+ ">"
|
|
)
|
|
|
|
|
|
class ExpandRightRule(RegexpChunkRule):
|
|
"""
|
|
A rule specifying how to expand chunks in a ``ChunkString`` to the
|
|
right, using two matching tag patterns: a left pattern, and a
|
|
right pattern. When applied to a ``ChunkString``, it will find any
|
|
chunk whose end matches left pattern, and immediately followed by
|
|
a strip whose beginning matches right pattern. It will then
|
|
expand the chunk to incorporate the new material on the right.
|
|
"""
|
|
|
|
def __init__(self, left_tag_pattern, right_tag_pattern, descr):
|
|
"""
|
|
Construct a new ``ExpandRightRule``.
|
|
|
|
:type right_tag_pattern: str
|
|
:param right_tag_pattern: This rule's right tag
|
|
pattern. When applied to a ``ChunkString``, this
|
|
rule will find any chunk whose end matches
|
|
``left_tag_pattern``, and immediately followed by a strip
|
|
whose beginning matches this pattern. It will
|
|
then merge those two chunks into a single chunk.
|
|
:type left_tag_pattern: str
|
|
:param left_tag_pattern: This rule's left tag
|
|
pattern. When applied to a ``ChunkString``, this
|
|
rule will find any chunk whose end matches
|
|
this pattern, and immediately followed by a strip
|
|
whose beginning matches ``right_tag_pattern``. It will
|
|
then expand the chunk to incorporate the new material on the right.
|
|
|
|
:type descr: str
|
|
:param descr: A short description of the purpose and/or effect
|
|
of this rule.
|
|
"""
|
|
# Ensure that the individual patterns are coherent. E.g., if
|
|
# left='(' and right=')', then this will raise an exception:
|
|
re.compile(tag_pattern2re_pattern(left_tag_pattern))
|
|
re.compile(tag_pattern2re_pattern(right_tag_pattern))
|
|
|
|
self._left_tag_pattern = left_tag_pattern
|
|
self._right_tag_pattern = right_tag_pattern
|
|
regexp = re.compile(
|
|
r"(?P<left>%s)\}(?P<right>%s)"
|
|
% (
|
|
tag_pattern2re_pattern(left_tag_pattern),
|
|
tag_pattern2re_pattern(right_tag_pattern),
|
|
)
|
|
)
|
|
RegexpChunkRule.__init__(self, regexp, r"\g<left>\g<right>}", descr)
|
|
|
|
def __repr__(self):
|
|
"""
|
|
Return a string representation of this rule. It has the form::
|
|
|
|
<ExpandRightRule: '<NN|DT|JJ>', '<NN|JJ>'>
|
|
|
|
Note that this representation does not include the
|
|
description string; that string can be accessed
|
|
separately with the ``descr()`` method.
|
|
|
|
:rtype: str
|
|
"""
|
|
return (
|
|
"<ExpandRightRule: "
|
|
+ repr(self._left_tag_pattern)
|
|
+ ", "
|
|
+ repr(self._right_tag_pattern)
|
|
+ ">"
|
|
)
|
|
|
|
|
|
class ChunkRuleWithContext(RegexpChunkRule):
|
|
"""
|
|
A rule specifying how to add chunks to a ``ChunkString``, using
|
|
three matching tag patterns: one for the left context, one for the
|
|
chunk, and one for the right context. When applied to a
|
|
``ChunkString``, it will find any substring that matches the chunk
|
|
tag pattern, is surrounded by substrings that match the two
|
|
context patterns, and is not already part of a chunk; and create a
|
|
new chunk containing the substring that matched the chunk tag
|
|
pattern.
|
|
|
|
Caveat: Both the left and right context are consumed when this
|
|
rule matches; therefore, if you need to find overlapping matches,
|
|
you will need to apply your rule more than once.
|
|
"""
|
|
|
|
def __init__(
|
|
self,
|
|
left_context_tag_pattern,
|
|
chunk_tag_pattern,
|
|
right_context_tag_pattern,
|
|
descr,
|
|
):
|
|
"""
|
|
Construct a new ``ChunkRuleWithContext``.
|
|
|
|
:type left_context_tag_pattern: str
|
|
:param left_context_tag_pattern: A tag pattern that must match
|
|
the left context of ``chunk_tag_pattern`` for this rule to
|
|
apply.
|
|
:type chunk_tag_pattern: str
|
|
:param chunk_tag_pattern: A tag pattern that must match for this
|
|
rule to apply. If the rule does apply, then this pattern
|
|
also identifies the substring that will be made into a chunk.
|
|
:type right_context_tag_pattern: str
|
|
:param right_context_tag_pattern: A tag pattern that must match
|
|
the right context of ``chunk_tag_pattern`` for this rule to
|
|
apply.
|
|
:type descr: str
|
|
:param descr: A short description of the purpose and/or effect
|
|
of this rule.
|
|
"""
|
|
# Ensure that the individual patterns are coherent. E.g., if
|
|
# left='(' and right=')', then this will raise an exception:
|
|
re.compile(tag_pattern2re_pattern(left_context_tag_pattern))
|
|
re.compile(tag_pattern2re_pattern(chunk_tag_pattern))
|
|
re.compile(tag_pattern2re_pattern(right_context_tag_pattern))
|
|
|
|
self._left_context_tag_pattern = left_context_tag_pattern
|
|
self._chunk_tag_pattern = chunk_tag_pattern
|
|
self._right_context_tag_pattern = right_context_tag_pattern
|
|
regexp = re.compile(
|
|
"(?P<left>%s)(?P<chunk>%s)(?P<right>%s)%s"
|
|
% (
|
|
tag_pattern2re_pattern(left_context_tag_pattern),
|
|
tag_pattern2re_pattern(chunk_tag_pattern),
|
|
tag_pattern2re_pattern(right_context_tag_pattern),
|
|
ChunkString.IN_STRIP_PATTERN,
|
|
)
|
|
)
|
|
replacement = r"\g<left>{\g<chunk>}\g<right>"
|
|
RegexpChunkRule.__init__(self, regexp, replacement, descr)
|
|
|
|
def __repr__(self):
|
|
"""
|
|
Return a string representation of this rule. It has the form::
|
|
|
|
<ChunkRuleWithContext: '<IN>', '<NN>', '<DT>'>
|
|
|
|
Note that this representation does not include the
|
|
description string; that string can be accessed
|
|
separately with the ``descr()`` method.
|
|
|
|
:rtype: str
|
|
"""
|
|
return "<ChunkRuleWithContext: {!r}, {!r}, {!r}>".format(
|
|
self._left_context_tag_pattern,
|
|
self._chunk_tag_pattern,
|
|
self._right_context_tag_pattern,
|
|
)
|
|
|
|
|
|
# //////////////////////////////////////////////////////
|
|
# Tag Pattern Format Conversion
|
|
# //////////////////////////////////////////////////////
|
|
|
|
# this should probably be made more strict than it is -- e.g., it
|
|
# currently accepts 'foo'.
|
|
CHUNK_TAG_PATTERN = re.compile(
|
|
r"^(({}|<{}>)*)$".format(r"([^\{\}<>]|\{\d+,?\}|\{\d*,\d+\})+", r"[^\{\}<>]+")
|
|
)
|
|
|
|
|
|
def tag_pattern2re_pattern(tag_pattern):
|
|
"""
|
|
Convert a tag pattern to a regular expression pattern. A "tag
|
|
pattern" is a modified version of a regular expression, designed
|
|
for matching sequences of tags. The differences between regular
|
|
expression patterns and tag patterns are:
|
|
|
|
- In tag patterns, ``'<'`` and ``'>'`` act as parentheses; so
|
|
``'<NN>+'`` matches one or more repetitions of ``'<NN>'``, not
|
|
``'<NN'`` followed by one or more repetitions of ``'>'``.
|
|
- Whitespace in tag patterns is ignored. So
|
|
``'<DT> | <NN>'`` is equivalent to ``'<DT>|<NN>'``
|
|
- In tag patterns, ``'.'`` is equivalent to ``'[^{}<>]'``; so
|
|
``'<NN.*>'`` matches any single tag starting with ``'NN'``.
|
|
|
|
In particular, ``tag_pattern2re_pattern`` performs the following
|
|
transformations on the given pattern:
|
|
|
|
- Replace '.' with '[^<>{}]'
|
|
- Remove any whitespace
|
|
- Add extra parens around '<' and '>', to make '<' and '>' act
|
|
like parentheses. E.g., so that in '<NN>+', the '+' has scope
|
|
over the entire '<NN>'; and so that in '<NN|IN>', the '|' has
|
|
scope over 'NN' and 'IN', but not '<' or '>'.
|
|
- Check to make sure the resulting pattern is valid.
|
|
|
|
:type tag_pattern: str
|
|
:param tag_pattern: The tag pattern to convert to a regular
|
|
expression pattern.
|
|
:raise ValueError: If ``tag_pattern`` is not a valid tag pattern.
|
|
In particular, ``tag_pattern`` should not include braces; and it
|
|
should not contain nested or mismatched angle-brackets.
|
|
:rtype: str
|
|
:return: A regular expression pattern corresponding to
|
|
``tag_pattern``.
|
|
"""
|
|
# Clean up the regular expression
|
|
tag_pattern = re.sub(r"\s", "", tag_pattern)
|
|
tag_pattern = re.sub(r"<", "(<(", tag_pattern)
|
|
tag_pattern = re.sub(r">", ")>)", tag_pattern)
|
|
|
|
# Check the regular expression
|
|
if not CHUNK_TAG_PATTERN.match(tag_pattern):
|
|
raise ValueError("Bad tag pattern: %r" % tag_pattern)
|
|
|
|
# Replace "." with CHUNK_TAG_CHAR.
|
|
# We have to do this after, since it adds {}[]<>s, which would
|
|
# confuse CHUNK_TAG_PATTERN.
|
|
# PRE doesn't have lookback assertions, so reverse twice, and do
|
|
# the pattern backwards (with lookahead assertions). This can be
|
|
# made much cleaner once we can switch back to SRE.
|
|
def reverse_str(str):
|
|
lst = list(str)
|
|
lst.reverse()
|
|
return "".join(lst)
|
|
|
|
tc_rev = reverse_str(ChunkString.CHUNK_TAG_CHAR)
|
|
reversed = reverse_str(tag_pattern)
|
|
reversed = re.sub(r"\.(?!\\(\\\\)*($|[^\\]))", tc_rev, reversed)
|
|
tag_pattern = reverse_str(reversed)
|
|
|
|
return tag_pattern
|
|
|
|
|
|
# //////////////////////////////////////////////////////
|
|
# RegexpChunkParser
|
|
# //////////////////////////////////////////////////////
|
|
|
|
|
|
class RegexpChunkParser(ChunkParserI):
|
|
"""
|
|
A regular expression based chunk parser. ``RegexpChunkParser`` uses a
|
|
sequence of "rules" to find chunks of a single type within a
|
|
text. The chunking of the text is encoded using a ``ChunkString``,
|
|
and each rule acts by modifying the chunking in the
|
|
``ChunkString``. The rules are all implemented using regular
|
|
expression matching and substitution.
|
|
|
|
The ``RegexpChunkRule`` class and its subclasses (``ChunkRule``,
|
|
``StripRule``, ``UnChunkRule``, ``MergeRule``, and ``SplitRule``)
|
|
define the rules that are used by ``RegexpChunkParser``. Each rule
|
|
defines an ``apply()`` method, which modifies the chunking encoded
|
|
by a given ``ChunkString``.
|
|
|
|
:type _rules: list(RegexpChunkRule)
|
|
:ivar _rules: The list of rules that should be applied to a text.
|
|
:type _trace: int
|
|
:ivar _trace: The default level of tracing.
|
|
|
|
"""
|
|
|
|
def __init__(self, rules, chunk_label="NP", root_label="S", trace=0):
|
|
"""
|
|
Construct a new ``RegexpChunkParser``.
|
|
|
|
:type rules: list(RegexpChunkRule)
|
|
:param rules: The sequence of rules that should be used to
|
|
generate the chunking for a tagged text.
|
|
:type chunk_label: str
|
|
:param chunk_label: The node value that should be used for
|
|
chunk subtrees. This is typically a short string
|
|
describing the type of information contained by the chunk,
|
|
such as ``"NP"`` for base noun phrases.
|
|
:type root_label: str
|
|
:param root_label: The node value that should be used for the
|
|
top node of the chunk structure.
|
|
:type trace: int
|
|
:param trace: The level of tracing that should be used when
|
|
parsing a text. ``0`` will generate no tracing output;
|
|
``1`` will generate normal tracing output; and ``2`` or
|
|
higher will generate verbose tracing output.
|
|
"""
|
|
self._rules = rules
|
|
self._trace = trace
|
|
self._chunk_label = chunk_label
|
|
self._root_label = root_label
|
|
|
|
def _trace_apply(self, chunkstr, verbose):
|
|
"""
|
|
Apply each rule of this ``RegexpChunkParser`` to ``chunkstr``, in
|
|
turn. Generate trace output between each rule. If ``verbose``
|
|
is true, then generate verbose output.
|
|
|
|
:type chunkstr: ChunkString
|
|
:param chunkstr: The chunk string to which each rule should be
|
|
applied.
|
|
:type verbose: bool
|
|
:param verbose: Whether output should be verbose.
|
|
:rtype: None
|
|
"""
|
|
print("# Input:")
|
|
print(chunkstr)
|
|
for rule in self._rules:
|
|
rule.apply(chunkstr)
|
|
if verbose:
|
|
print("#", rule.descr() + " (" + repr(rule) + "):")
|
|
else:
|
|
print("#", rule.descr() + ":")
|
|
print(chunkstr)
|
|
|
|
def _notrace_apply(self, chunkstr):
|
|
"""
|
|
Apply each rule of this ``RegexpChunkParser`` to ``chunkstr``, in
|
|
turn.
|
|
|
|
:param chunkstr: The chunk string to which each rule should be
|
|
applied.
|
|
:type chunkstr: ChunkString
|
|
:rtype: None
|
|
"""
|
|
|
|
for rule in self._rules:
|
|
rule.apply(chunkstr)
|
|
|
|
def parse(self, chunk_struct, trace=None):
|
|
"""
|
|
:type chunk_struct: Tree
|
|
:param chunk_struct: the chunk structure to be (further) chunked
|
|
:type trace: int
|
|
:param trace: The level of tracing that should be used when
|
|
parsing a text. ``0`` will generate no tracing output;
|
|
``1`` will generate normal tracing output; and ``2`` or
|
|
higher will generate verbose tracing output. This value
|
|
overrides the trace level value that was given to the
|
|
constructor.
|
|
:rtype: Tree
|
|
:return: a chunk structure that encodes the chunks in a given
|
|
tagged sentence. A chunk is a non-overlapping linguistic
|
|
group, such as a noun phrase. The set of chunks
|
|
identified in the chunk structure depends on the rules
|
|
used to define this ``RegexpChunkParser``.
|
|
"""
|
|
if len(chunk_struct) == 0:
|
|
print("Warning: parsing empty text")
|
|
return Tree(self._root_label, [])
|
|
|
|
try:
|
|
chunk_struct.label()
|
|
except AttributeError:
|
|
chunk_struct = Tree(self._root_label, chunk_struct)
|
|
|
|
# Use the default trace value?
|
|
if trace is None:
|
|
trace = self._trace
|
|
|
|
chunkstr = ChunkString(chunk_struct)
|
|
|
|
# Apply the sequence of rules to the chunkstring.
|
|
if trace:
|
|
verbose = trace > 1
|
|
self._trace_apply(chunkstr, verbose)
|
|
else:
|
|
self._notrace_apply(chunkstr)
|
|
|
|
# Use the chunkstring to create a chunk structure.
|
|
return chunkstr.to_chunkstruct(self._chunk_label)
|
|
|
|
def rules(self):
|
|
"""
|
|
:return: the sequence of rules used by ``RegexpChunkParser``.
|
|
:rtype: list(RegexpChunkRule)
|
|
"""
|
|
return self._rules
|
|
|
|
def __repr__(self):
|
|
"""
|
|
:return: a concise string representation of this
|
|
``RegexpChunkParser``.
|
|
:rtype: str
|
|
"""
|
|
return "<RegexpChunkParser with %d rules>" % len(self._rules)
|
|
|
|
def __str__(self):
|
|
"""
|
|
:return: a verbose string representation of this ``RegexpChunkParser``.
|
|
:rtype: str
|
|
"""
|
|
s = "RegexpChunkParser with %d rules:\n" % len(self._rules)
|
|
margin = 0
|
|
for rule in self._rules:
|
|
margin = max(margin, len(rule.descr()))
|
|
if margin < 35:
|
|
format = " %" + repr(-(margin + 3)) + "s%s\n"
|
|
else:
|
|
format = " %s\n %s\n"
|
|
for rule in self._rules:
|
|
s += format % (rule.descr(), repr(rule))
|
|
return s[:-1]
|
|
|
|
|
|
# //////////////////////////////////////////////////////
|
|
# Chunk Grammar
|
|
# //////////////////////////////////////////////////////
|
|
|
|
|
|
class RegexpParser(ChunkParserI):
|
|
r"""
|
|
A grammar based chunk parser. ``chunk.RegexpParser`` uses a set of
|
|
regular expression patterns to specify the behavior of the parser.
|
|
The chunking of the text is encoded using a ``ChunkString``, and
|
|
each rule acts by modifying the chunking in the ``ChunkString``.
|
|
The rules are all implemented using regular expression matching
|
|
and substitution.
|
|
|
|
A grammar contains one or more clauses in the following form::
|
|
|
|
NP:
|
|
{<DT|JJ>} # chunk determiners and adjectives
|
|
}<[\.VI].*>+{ # strip any tag beginning with V, I, or .
|
|
<.*>}{<DT> # split a chunk at a determiner
|
|
<DT|JJ>{}<NN.*> # merge chunk ending with det/adj
|
|
# with one starting with a noun
|
|
|
|
The patterns of a clause are executed in order. An earlier
|
|
pattern may introduce a chunk boundary that prevents a later
|
|
pattern from executing. Sometimes an individual pattern will
|
|
match on multiple, overlapping extents of the input. As with
|
|
regular expression substitution more generally, the chunker will
|
|
identify the first match possible, then continue looking for matches
|
|
after this one has ended.
|
|
|
|
The clauses of a grammar are also executed in order. A cascaded
|
|
chunk parser is one having more than one clause. The maximum depth
|
|
of a parse tree created by this chunk parser is the same as the
|
|
number of clauses in the grammar.
|
|
|
|
When tracing is turned on, the comment portion of a line is displayed
|
|
each time the corresponding pattern is applied.
|
|
|
|
:type _start: str
|
|
:ivar _start: The start symbol of the grammar (the root node of
|
|
resulting trees)
|
|
:type _stages: int
|
|
:ivar _stages: The list of parsing stages corresponding to the grammar
|
|
|
|
"""
|
|
|
|
def __init__(self, grammar, root_label="S", loop=1, trace=0):
|
|
"""
|
|
Create a new chunk parser, from the given start state
|
|
and set of chunk patterns.
|
|
|
|
:param grammar: The grammar, or a list of RegexpChunkParser objects
|
|
:type grammar: str or list(RegexpChunkParser)
|
|
:param root_label: The top node of the tree being created
|
|
:type root_label: str or Nonterminal
|
|
:param loop: The number of times to run through the patterns
|
|
:type loop: int
|
|
:type trace: int
|
|
:param trace: The level of tracing that should be used when
|
|
parsing a text. ``0`` will generate no tracing output;
|
|
``1`` will generate normal tracing output; and ``2`` or
|
|
higher will generate verbose tracing output.
|
|
"""
|
|
self._trace = trace
|
|
self._stages = []
|
|
self._grammar = grammar
|
|
self._loop = loop
|
|
|
|
if isinstance(grammar, str):
|
|
self._read_grammar(grammar, root_label, trace)
|
|
else:
|
|
# Make sur the grammar looks like it has the right type:
|
|
type_err = (
|
|
"Expected string or list of RegexpChunkParsers " "for the grammar."
|
|
)
|
|
try:
|
|
grammar = list(grammar)
|
|
except BaseException as e:
|
|
raise TypeError(type_err) from e
|
|
for elt in grammar:
|
|
if not isinstance(elt, RegexpChunkParser):
|
|
raise TypeError(type_err)
|
|
self._stages = grammar
|
|
|
|
def _read_grammar(self, grammar, root_label, trace):
|
|
"""
|
|
Helper function for __init__: read the grammar if it is a
|
|
string.
|
|
"""
|
|
rules = []
|
|
lhs = None
|
|
pattern = regex.compile("(?P<nonterminal>(\\.|[^:])*)(:(?P<rule>.*))")
|
|
for line in grammar.split("\n"):
|
|
line = line.strip()
|
|
|
|
# New stage begins if there's an unescaped ':'
|
|
m = pattern.match(line)
|
|
if m:
|
|
# Record the stage that we just completed.
|
|
self._add_stage(rules, lhs, root_label, trace)
|
|
# Start a new stage.
|
|
lhs = m.group("nonterminal").strip()
|
|
rules = []
|
|
line = m.group("rule").strip()
|
|
|
|
# Skip blank & comment-only lines
|
|
if line == "" or line.startswith("#"):
|
|
continue
|
|
|
|
# Add the rule
|
|
rules.append(RegexpChunkRule.fromstring(line))
|
|
|
|
# Record the final stage
|
|
self._add_stage(rules, lhs, root_label, trace)
|
|
|
|
def _add_stage(self, rules, lhs, root_label, trace):
|
|
"""
|
|
Helper function for __init__: add a new stage to the parser.
|
|
"""
|
|
if rules != []:
|
|
if not lhs:
|
|
raise ValueError("Expected stage marker (eg NP:)")
|
|
parser = RegexpChunkParser(
|
|
rules, chunk_label=lhs, root_label=root_label, trace=trace
|
|
)
|
|
self._stages.append(parser)
|
|
|
|
def parse(self, chunk_struct, trace=None):
|
|
"""
|
|
Apply the chunk parser to this input.
|
|
|
|
:type chunk_struct: Tree
|
|
:param chunk_struct: the chunk structure to be (further) chunked
|
|
(this tree is modified, and is also returned)
|
|
:type trace: int
|
|
:param trace: The level of tracing that should be used when
|
|
parsing a text. ``0`` will generate no tracing output;
|
|
``1`` will generate normal tracing output; and ``2`` or
|
|
higher will generate verbose tracing output. This value
|
|
overrides the trace level value that was given to the
|
|
constructor.
|
|
:return: the chunked output.
|
|
:rtype: Tree
|
|
"""
|
|
if trace is None:
|
|
trace = self._trace
|
|
for i in range(self._loop):
|
|
for parser in self._stages:
|
|
chunk_struct = parser.parse(chunk_struct, trace=trace)
|
|
return chunk_struct
|
|
|
|
def __repr__(self):
|
|
"""
|
|
:return: a concise string representation of this ``chunk.RegexpParser``.
|
|
:rtype: str
|
|
"""
|
|
return "<chunk.RegexpParser with %d stages>" % len(self._stages)
|
|
|
|
def __str__(self):
|
|
"""
|
|
:return: a verbose string representation of this
|
|
``RegexpParser``.
|
|
:rtype: str
|
|
"""
|
|
s = "chunk.RegexpParser with %d stages:\n" % len(self._stages)
|
|
margin = 0
|
|
for parser in self._stages:
|
|
s += "%s\n" % parser
|
|
return s[:-1]
|
|
|
|
|
|
# //////////////////////////////////////////////////////
|
|
# Demonstration code
|
|
# //////////////////////////////////////////////////////
|
|
|
|
|
|
def demo_eval(chunkparser, text):
|
|
"""
|
|
Demonstration code for evaluating a chunk parser, using a
|
|
``ChunkScore``. This function assumes that ``text`` contains one
|
|
sentence per line, and that each sentence has the form expected by
|
|
``tree.chunk``. It runs the given chunk parser on each sentence in
|
|
the text, and scores the result. It prints the final score
|
|
(precision, recall, and f-measure); and reports the set of chunks
|
|
that were missed and the set of chunks that were incorrect. (At
|
|
most 10 missing chunks and 10 incorrect chunks are reported).
|
|
|
|
:param chunkparser: The chunkparser to be tested
|
|
:type chunkparser: ChunkParserI
|
|
:param text: The chunked tagged text that should be used for
|
|
evaluation.
|
|
:type text: str
|
|
"""
|
|
from nltk import chunk
|
|
from nltk.tree import Tree
|
|
|
|
# Evaluate our chunk parser.
|
|
chunkscore = chunk.ChunkScore()
|
|
|
|
for sentence in text.split("\n"):
|
|
print(sentence)
|
|
sentence = sentence.strip()
|
|
if not sentence:
|
|
continue
|
|
gold = chunk.tagstr2tree(sentence)
|
|
tokens = gold.leaves()
|
|
test = chunkparser.parse(Tree("S", tokens), trace=1)
|
|
chunkscore.score(gold, test)
|
|
print()
|
|
|
|
print("/" + ("=" * 75) + "\\")
|
|
print("Scoring", chunkparser)
|
|
print("-" * 77)
|
|
print("Precision: %5.1f%%" % (chunkscore.precision() * 100), " " * 4, end=" ")
|
|
print("Recall: %5.1f%%" % (chunkscore.recall() * 100), " " * 6, end=" ")
|
|
print("F-Measure: %5.1f%%" % (chunkscore.f_measure() * 100))
|
|
|
|
# Missed chunks.
|
|
if chunkscore.missed():
|
|
print("Missed:")
|
|
missed = chunkscore.missed()
|
|
for chunk in missed[:10]:
|
|
print(" ", " ".join(map(str, chunk)))
|
|
if len(chunkscore.missed()) > 10:
|
|
print(" ...")
|
|
|
|
# Incorrect chunks.
|
|
if chunkscore.incorrect():
|
|
print("Incorrect:")
|
|
incorrect = chunkscore.incorrect()
|
|
for chunk in incorrect[:10]:
|
|
print(" ", " ".join(map(str, chunk)))
|
|
if len(chunkscore.incorrect()) > 10:
|
|
print(" ...")
|
|
|
|
print("\\" + ("=" * 75) + "/")
|
|
print()
|
|
|
|
|
|
def demo():
|
|
"""
|
|
A demonstration for the ``RegexpChunkParser`` class. A single text is
|
|
parsed with four different chunk parsers, using a variety of rules
|
|
and strategies.
|
|
"""
|
|
|
|
from nltk import Tree, chunk
|
|
|
|
text = """\
|
|
[ the/DT little/JJ cat/NN ] sat/VBD on/IN [ the/DT mat/NN ] ./.
|
|
[ John/NNP ] saw/VBD [the/DT cats/NNS] [the/DT dog/NN] chased/VBD ./.
|
|
[ John/NNP ] thinks/VBZ [ Mary/NN ] saw/VBD [ the/DT cat/NN ] sit/VB on/IN [ the/DT mat/NN ]./.
|
|
"""
|
|
|
|
print("*" * 75)
|
|
print("Evaluation text:")
|
|
print(text)
|
|
print("*" * 75)
|
|
print()
|
|
|
|
grammar = r"""
|
|
NP: # NP stage
|
|
{<DT>?<JJ>*<NN>} # chunk determiners, adjectives and nouns
|
|
{<NNP>+} # chunk proper nouns
|
|
"""
|
|
cp = chunk.RegexpParser(grammar)
|
|
demo_eval(cp, text)
|
|
|
|
grammar = r"""
|
|
NP:
|
|
{<.*>} # start by chunking each tag
|
|
}<[\.VI].*>+{ # unchunk any verbs, prepositions or periods
|
|
<DT|JJ>{}<NN.*> # merge det/adj with nouns
|
|
"""
|
|
cp = chunk.RegexpParser(grammar)
|
|
demo_eval(cp, text)
|
|
|
|
grammar = r"""
|
|
NP: {<DT>?<JJ>*<NN>} # chunk determiners, adjectives and nouns
|
|
VP: {<TO>?<VB.*>} # VP = verb words
|
|
"""
|
|
cp = chunk.RegexpParser(grammar)
|
|
demo_eval(cp, text)
|
|
|
|
grammar = r"""
|
|
NP: {<.*>*} # start by chunking everything
|
|
}<[\.VI].*>+{ # strip any verbs, prepositions or periods
|
|
<.*>}{<DT> # separate on determiners
|
|
PP: {<IN><NP>} # PP = preposition + noun phrase
|
|
VP: {<VB.*><NP|PP>*} # VP = verb words + NPs and PPs
|
|
"""
|
|
cp = chunk.RegexpParser(grammar)
|
|
demo_eval(cp, text)
|
|
|
|
# Evaluation
|
|
|
|
from nltk.corpus import conll2000
|
|
|
|
print()
|
|
print("Demonstration of empty grammar:")
|
|
|
|
cp = chunk.RegexpParser("")
|
|
print(chunk.accuracy(cp, conll2000.chunked_sents("test.txt", chunk_types=("NP",))))
|
|
|
|
print()
|
|
print("Demonstration of accuracy evaluation using CoNLL tags:")
|
|
|
|
grammar = r"""
|
|
NP:
|
|
{<.*>} # start by chunking each tag
|
|
}<[\.VI].*>+{ # unchunk any verbs, prepositions or periods
|
|
<DT|JJ>{}<NN.*> # merge det/adj with nouns
|
|
"""
|
|
cp = chunk.RegexpParser(grammar)
|
|
print(chunk.accuracy(cp, conll2000.chunked_sents("test.txt")[:5]))
|
|
|
|
print()
|
|
print("Demonstration of tagged token input")
|
|
|
|
grammar = r"""
|
|
NP: {<.*>*} # start by chunking everything
|
|
}<[\.VI].*>+{ # strip any verbs, prepositions or periods
|
|
<.*>}{<DT> # separate on determiners
|
|
PP: {<IN><NP>} # PP = preposition + noun phrase
|
|
VP: {<VB.*><NP|PP>*} # VP = verb words + NPs and PPs
|
|
"""
|
|
cp = chunk.RegexpParser(grammar)
|
|
print(
|
|
cp.parse(
|
|
[
|
|
("the", "DT"),
|
|
("little", "JJ"),
|
|
("cat", "NN"),
|
|
("sat", "VBD"),
|
|
("on", "IN"),
|
|
("the", "DT"),
|
|
("mat", "NN"),
|
|
(".", "."),
|
|
]
|
|
)
|
|
)
|
|
|
|
|
|
if __name__ == "__main__":
|
|
demo()
|