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85ecdab077
This simplest solution doesn't drop HTML from metadata when merging Elements from HTML input. We still need to address how to handle nested elements, and if we want to have `LayoutElements` in the metadata of Composite Elements, a unit test showing the current behavior. Note: metadata still contains `orig_elements` which has all the metadata.
1266 lines
55 KiB
Python
1266 lines
55 KiB
Python
"""Chunking objects not specific to a particular chunking strategy."""
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from __future__ import annotations
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import collections
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import copy
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from typing import Any, Callable, DefaultDict, Iterable, Iterator, cast
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import regex
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from typing_extensions import Self, TypeAlias
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from unstructured.common.html_table import HtmlCell, HtmlRow, HtmlTable
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from unstructured.documents.elements import (
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CompositeElement,
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ConsolidationStrategy,
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Element,
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ElementMetadata,
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Table,
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TableChunk,
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Title,
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)
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from unstructured.utils import lazyproperty
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# ================================================================================================
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# MODEL
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# ================================================================================================
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CHUNK_MAX_CHARS_DEFAULT: int = 500
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"""Hard-max chunk-length when no explicit value specified in `max_characters` argument.
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Provided for reference only, for example so the ingest CLI can advertise the default value in its
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UI. External chunking-related functions (e.g. in ingest or decorators) should use
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`max_characters: int | None = None` and not apply this default themselves. Only
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`ChunkingOptions.max_characters` should apply a default value.
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"""
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CHUNK_MULTI_PAGE_DEFAULT: bool = True
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"""When False, respect page-boundaries (no two elements from different page in same chunk).
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Only operative for "by_title" chunking strategy.
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"""
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BoundaryPredicate: TypeAlias = Callable[[Element], bool]
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"""Detects when element represents crossing a semantic boundary like section or page."""
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PreChunk: TypeAlias = "TablePreChunk | TextPreChunk"
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"""The kind of object produced by a pre-chunker."""
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TextAndHtml: TypeAlias = tuple[str, str]
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# ================================================================================================
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# CHUNKING OPTIONS
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# ================================================================================================
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class ChunkingOptions:
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"""Specifies parameters of optional chunking behaviors.
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Parameters
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----------
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max_characters
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Hard-maximum text-length of chunk. A chunk longer than this will be split mid-text and be
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emitted as two or more chunks.
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new_after_n_chars
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Preferred approximate chunk size. A chunk composed of elements totalling this size or
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greater is considered "full" and will not be enlarged by adding another element, even if it
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will fit within the remaining `max_characters` for that chunk. Defaults to `max_characters`
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when not specified, which effectively disables this behavior. Specifying 0 for this
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argument causes each element to appear in a chunk by itself (although an element with text
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longer than `max_characters` will be still be split into two or more chunks).
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combine_text_under_n_chars
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Provides a way to "recombine" small chunks formed by breaking on a semantic boundary. Only
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relevant for a chunking strategy that specifies higher-level semantic boundaries to be
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respected, like "section" or "page". Recursively combines two adjacent pre-chunks when the
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first pre-chunk is smaller than this threshold. "Recursively" here means the resulting
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pre-chunk can be combined with the next pre-chunk if it is still under the length threshold.
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Defaults to `max_characters` which combines chunks whenever space allows. Specifying 0 for
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this argument suppresses combining of small chunks. Note this value is "capped" at the
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`new_after_n_chars` value since a value higher than that would not change this parameter's
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effect.
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overlap
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Specifies the length of a string ("tail") to be drawn from each chunk and prefixed to the
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next chunk as a context-preserving mechanism. By default, this only applies to split-chunks
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where an oversized element is divided into multiple chunks by text-splitting.
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overlap_all
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Default: `False`. When `True`, apply overlap between "normal" chunks formed from whole
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elements and not subject to text-splitting. Use this with caution as it entails a certain
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level of "pollution" of otherwise clean semantic chunk boundaries.
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text_splitting_separators
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A sequence of strings like `("\n", " ")` to be used as target separators during
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text-splitting. Text-splitting only applies to splitting an oversized element into two or
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more chunks. These separators are tried in the specified order until one is found in the
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string to be split. The default separator is `""` which matches between any two characters.
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This separator should not be specified in this sequence because it is always the separator
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of last-resort. Note that because the separator is removed during text-splitting, only
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whitespace character sequences are suitable.
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"""
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def __init__(self, **kwargs: Any):
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self._kwargs = kwargs
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@classmethod
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def new(cls, **kwargs: Any) -> Self:
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"""Return instance or raises `ValueError` on invalid arguments like overlap > max_chars."""
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self = cls(**kwargs)
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self._validate()
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return self
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@lazyproperty
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def boundary_predicates(self) -> tuple[BoundaryPredicate, ...]:
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"""The semantic-boundary detectors to be applied to break pre-chunks.
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Overridden by sub-typs to provide semantic-boundary isolation behaviors.
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"""
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return ()
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@lazyproperty
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def combine_text_under_n_chars(self) -> int:
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"""Combine two consecutive text pre-chunks if first is smaller than this and both will fit.
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Default applied here is `0` which essentially disables chunk combining. Must be overridden
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by subclass where combining behavior is supported.
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"""
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arg_value = self._kwargs.get("combine_text_under_n_chars")
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return arg_value if arg_value is not None else 0
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@lazyproperty
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def hard_max(self) -> int:
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"""The maximum size for a chunk.
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A pre-chunk will only exceed this size when it contains exactly one element which by itself
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exceeds this size. Such a pre-chunk is subject to mid-text splitting later in the chunking
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process.
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"""
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arg_value = self._kwargs.get("max_characters")
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return arg_value if arg_value is not None else CHUNK_MAX_CHARS_DEFAULT
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@lazyproperty
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def include_orig_elements(self) -> bool:
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"""When True, add original elements from pre-chunk to `.metadata.orig_elements` of chunk.
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Default value is `True`.
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"""
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arg_value = self._kwargs.get("include_orig_elements")
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return True if arg_value is None else bool(arg_value)
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@lazyproperty
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def inter_chunk_overlap(self) -> int:
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"""Characters of overlap to add between chunks.
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This applies only to boundaries between chunks formed from whole elements and not to
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text-splitting boundaries that arise from splitting an oversized element.
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"""
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overlap_all_arg = self._kwargs.get("overlap_all")
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return self.overlap if overlap_all_arg else 0
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@lazyproperty
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def overlap(self) -> int:
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"""The number of characters to overlap text when splitting chunks mid-text.
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The actual overlap will not exceed this number of characters but may be less as required to
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respect splitting-character boundaries.
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"""
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overlap_arg = self._kwargs.get("overlap")
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return overlap_arg or 0
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@lazyproperty
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def soft_max(self) -> int:
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"""A pre-chunk of this size or greater is considered full.
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Note that while a value of `0` is valid, it essentially disables chunking by putting
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each element into its own chunk.
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"""
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hard_max = self.hard_max
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new_after_n_chars_arg = self._kwargs.get("new_after_n_chars")
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# -- default value is == max_characters --
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if new_after_n_chars_arg is None:
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return hard_max
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# -- new_after_n_chars > max_characters behaves the same as ==max_characters --
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if new_after_n_chars_arg > hard_max:
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return hard_max
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# -- otherwise, give them what they asked for --
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return new_after_n_chars_arg
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@lazyproperty
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def split(self) -> Callable[[str], tuple[str, str]]:
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"""A text-splitting function suitable for splitting the text of an oversized pre-chunk.
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The function is pre-configured with the chosen chunking window size and any other applicable
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options specified by the caller as part of this chunking-options instance.
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"""
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return _TextSplitter(self)
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@lazyproperty
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def text_separator(self) -> str:
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"""The string to insert between elements when concatenating their text for a chunk.
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Right now this is just "\n\n" (a blank line in plain text), but having this here rather
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than as a module-level constant provides a way for us to easily make it user-configurable
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in future if we want to.
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"""
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return "\n\n"
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@lazyproperty
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def text_splitting_separators(self) -> tuple[str, ...]:
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"""Sequence of text-splitting target strings to be used in order of preference."""
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text_splitting_separators_arg = self._kwargs.get("text_splitting_separators")
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return (
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("\n", " ")
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if text_splitting_separators_arg is None
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else tuple(text_splitting_separators_arg)
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)
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def _validate(self) -> None:
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"""Raise ValueError if requestion option-set is invalid."""
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max_characters = self.hard_max
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# -- chunking window must have positive length --
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if max_characters <= 0:
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raise ValueError(f"'max_characters' argument must be > 0," f" got {max_characters}")
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# -- a negative value for `new_after_n_chars` is assumed to be a mistake the caller will
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# -- want to know about
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new_after_n_chars = self._kwargs.get("new_after_n_chars")
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if new_after_n_chars is not None and new_after_n_chars < 0:
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raise ValueError(
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f"'new_after_n_chars' argument must be >= 0," f" got {new_after_n_chars}"
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)
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# -- overlap must be less than max-chars or the chunk text will never be consumed --
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if self.overlap >= max_characters:
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raise ValueError(
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f"'overlap' argument must be less than `max_characters`,"
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f" got {self.overlap} >= {max_characters}"
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)
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# ================================================================================================
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# PRE-CHUNKER
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# ================================================================================================
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class PreChunker:
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"""Gathers sequential elements into pre-chunks as length constraints allow.
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The pre-chunker's responsibilities are:
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- **Segregate semantic units.** Identify semantic unit boundaries and segregate elements on
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either side of those boundaries into different sections. In this case, the primary indicator
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of a semantic boundary is a `Title` element. A page-break (change in page-number) is also a
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semantic boundary when `multipage_sections` is `False`.
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- **Minimize chunk count for each semantic unit.** Group the elements within a semantic unit
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into sections as big as possible without exceeding the chunk window size.
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- **Minimize chunks that must be split mid-text.** Precompute the text length of each section
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and only produce a section that exceeds the chunk window size when there is a single element
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with text longer than that window.
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A Table element is placed into a section by itself. CheckBox elements are dropped.
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The "by-title" strategy specifies breaking on section boundaries; a `Title` element indicates
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a new "section", hence the "by-title" designation.
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"""
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def __init__(self, elements: Iterable[Element], opts: ChunkingOptions):
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self._elements = elements
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self._opts = opts
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@classmethod
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def iter_pre_chunks(
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cls, elements: Iterable[Element], opts: ChunkingOptions
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) -> Iterator[PreChunk]:
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"""Generate pre-chunks from the element-stream provided on construction."""
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return cls(elements, opts)._iter_pre_chunks()
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def _iter_pre_chunks(self) -> Iterator[PreChunk]:
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"""Generate pre-chunks from the element-stream provided on construction.
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A *pre-chunk* is the largest sub-sequence of elements that will both fit within the
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chunking window and respects the semantic boundary rules of the chunking strategy. When a
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single element exceeds the chunking window size it is placed in a pre-chunk by itself and
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is subject to mid-text splitting in the second phase of the chunking process.
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"""
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pre_chunk_builder = PreChunkBuilder(self._opts)
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for element in self._elements:
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# -- start new pre-chunk when necessary --
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if self._is_in_new_semantic_unit(element) or not pre_chunk_builder.will_fit(element):
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yield from pre_chunk_builder.flush()
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# -- add this element to the work-in-progress (WIP) pre-chunk --
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pre_chunk_builder.add_element(element)
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# -- flush "tail" pre-chunk, any partially-filled pre-chunk after last element is
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# -- processed
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yield from pre_chunk_builder.flush()
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@lazyproperty
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def _boundary_predicates(self) -> tuple[BoundaryPredicate, ...]:
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"""The semantic-boundary detectors to be applied to break pre-chunks."""
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return self._opts.boundary_predicates
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def _is_in_new_semantic_unit(self, element: Element) -> bool:
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"""True when `element` begins a new semantic unit such as a section or page."""
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# -- all detectors need to be called to update state and avoid double counting
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# -- boundaries that happen to coincide, like Table and new section on same element.
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# -- Using `any()` would short-circuit on first True.
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semantic_boundaries = [pred(element) for pred in self._boundary_predicates]
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return any(semantic_boundaries)
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class PreChunkBuilder:
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"""An element accumulator suitable for incrementally forming a pre-chunk.
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Provides the trial method `.will_fit()` a pre-chunker can use to determine whether it should add
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the next element in the element stream.
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`.flush()` is used to build a PreChunk object from the accumulated elements. This method
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returns an iterator that generates zero-or-one `TextPreChunk` or `TablePreChunk` object and is
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used like so:
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yield from builder.flush()
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If no elements have been accumulated, no `PreChunk` instance is generated. Flushing the builder
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clears the elements it contains so it is ready to build the next pre-chunk.
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"""
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def __init__(self, opts: ChunkingOptions) -> None:
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self._opts = opts
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self._separator_len = len(opts.text_separator)
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self._elements: list[Element] = []
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# -- overlap is only between pre-chunks so starts empty --
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self._overlap_prefix: str = ""
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# -- only includes non-empty element text, e.g. PageBreak.text=="" is not included --
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self._text_segments: list[str] = []
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# -- combined length of text-segments, not including separators --
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self._text_len: int = 0
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def add_element(self, element: Element) -> None:
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"""Add `element` to this section."""
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self._elements.append(element)
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if element.text:
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self._text_segments.append(element.text)
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self._text_len += len(element.text)
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def flush(self) -> Iterator[PreChunk]:
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"""Generate zero-or-one `PreChunk` object and clear the accumulator.
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Suitable for use to emit a PreChunk when the maximum size has been reached or a semantic
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boundary has been reached. Also to clear out a terminal pre-chunk at the end of an element
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stream.
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"""
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if not self._elements:
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return
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pre_chunk = (
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TablePreChunk(self._elements[0], self._overlap_prefix, self._opts)
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if isinstance(self._elements[0], Table)
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# -- copy list, don't use original or it may change contents as builder proceeds --
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else TextPreChunk(list(self._elements), self._overlap_prefix, self._opts)
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)
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# -- clear builder before yield so we're not sensitive to the timing of how/when this
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# -- iterator is exhausted and can add elements for the next pre-chunk immediately.
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self._reset_state(pre_chunk.overlap_tail)
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yield pre_chunk
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def will_fit(self, element: Element) -> bool:
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"""True when `element` can be added to this prechunk without violating its limits.
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There are several limits:
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- A `Table` element will never fit with any other element. It will only fit in an empty
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pre-chunk.
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- No element will fit in a pre-chunk that already contains a `Table` element.
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- A text-element will not fit in a pre-chunk that already exceeds the soft-max
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(aka. new_after_n_chars).
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- A text-element will not fit when together with the elements already present it would
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exceed the hard-max (aka. max_characters).
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"""
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# -- an empty pre-chunk will accept any element (including an oversized-element) --
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if len(self._elements) == 0:
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return True
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# -- a `Table` will not fit in a non-empty pre-chunk --
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if isinstance(element, Table):
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return False
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# -- no element will fit in a pre-chunk that already contains a `Table` element --
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if isinstance(self._elements[0], Table):
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return False
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# -- a pre-chunk that already exceeds the soft-max is considered "full" --
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if self._text_length > self._opts.soft_max:
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return False
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# -- don't add an element if it would increase total size beyond the hard-max --
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return not self._remaining_space < len(element.text)
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@property
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def _remaining_space(self) -> int:
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"""Maximum text-length of an element that can be added without exceeding maxlen."""
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# -- include length of trailing separator that will go before next element text --
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separators_len = self._separator_len * len(self._text_segments)
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return self._opts.hard_max - self._text_len - separators_len
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def _reset_state(self, overlap_prefix: str) -> None:
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"""Set working-state values back to "empty", ready to accumulate next pre-chunk."""
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self._overlap_prefix = overlap_prefix
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self._elements.clear()
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self._text_segments = [overlap_prefix] if overlap_prefix else []
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self._text_len = len(overlap_prefix)
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@property
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def _text_length(self) -> int:
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"""Length of the text in this pre-chunk.
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This value represents the chunk-size that would result if this pre-chunk was flushed in its
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current state. In particular, it does not include the length of a trailing separator (since
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that would only appear if an additional element was added).
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Not suitable for judging remaining space, use `.remaining_space` for that value.
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"""
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# -- number of text separators present in joined text of elements. This includes only
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# -- separators *between* text segments, not one at the end. Note there are zero separators
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# -- for both 0 and 1 text-segments.
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n = len(self._text_segments)
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separator_count = n - 1 if n else 0
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return self._text_len + (separator_count * self._separator_len)
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# ================================================================================================
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# PRE-CHUNK SUB-TYPES
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# ================================================================================================
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class TablePreChunk:
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"""A pre-chunk composed of a single Table element."""
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def __init__(self, table: Table, overlap_prefix: str, opts: ChunkingOptions) -> None:
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self._table = table
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self._overlap_prefix = overlap_prefix
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self._opts = opts
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def iter_chunks(self) -> Iterator[Table | TableChunk]:
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"""Split this pre-chunk into `Table` or `TableChunk` objects maxlen or smaller."""
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# -- A table with no non-whitespace text produces no chunks --
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if not self._table_text:
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return
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# -- only text-split a table when it's longer than the chunking window --
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maxlen = self._opts.hard_max
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if len(self._text_with_overlap) <= maxlen and len(self._html) <= maxlen:
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# -- use the compactified html for .text_as_html, even though we're not splitting --
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metadata = self._metadata
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metadata.text_as_html = self._html or None
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# -- note the overlap-prefix is prepended to its text --
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yield Table(text=self._text_with_overlap, metadata=metadata)
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return
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# -- When there's no HTML, split it like a normal element. Also fall back to text-only
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# -- chunks when `max_characters` is less than 50. `.text_as_html` metadata is impractical
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# -- for a chunking window that small because the 33 characterss of HTML overhead for each
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|
# -- chunk (`<table><tr><td>...</td></tr></table>`) would produce a very large number of
|
|
# -- very small chunks.
|
|
if not self._html or self._opts.hard_max < 50:
|
|
yield from self._iter_text_only_table_chunks()
|
|
return
|
|
|
|
# -- otherwise, form splits with "synchronized" text and html --
|
|
yield from self._iter_text_and_html_table_chunks()
|
|
|
|
@lazyproperty
|
|
def overlap_tail(self) -> str:
|
|
"""The portion of this chunk's text to be repeated as a prefix in the next chunk.
|
|
|
|
This value is the empty-string ("") when either the `.overlap` length option is `0` or
|
|
`.overlap_all` is `False`. When there is a text value, it is stripped of both leading and
|
|
trailing whitespace.
|
|
"""
|
|
overlap = self._opts.inter_chunk_overlap
|
|
return self._text_with_overlap[-overlap:].strip() if overlap else ""
|
|
|
|
@lazyproperty
|
|
def _html(self) -> str:
|
|
"""The compactified HTML for this table when it has text-as-HTML.
|
|
|
|
The empty string when table-structure has not been captured, perhaps because
|
|
`infer_table_structure` was set `False` in the partitioning call.
|
|
"""
|
|
if not (html_table := self._html_table):
|
|
return ""
|
|
|
|
return html_table.html
|
|
|
|
@lazyproperty
|
|
def _html_table(self) -> HtmlTable | None:
|
|
"""The `lxml` HTML element object for this table.
|
|
|
|
`None` when the `Table` element has no `.metadata.text_as_html`.
|
|
"""
|
|
if (text_as_html := self._table.metadata.text_as_html) is None:
|
|
return None
|
|
|
|
text_as_html = text_as_html.strip()
|
|
if not text_as_html: # pragma: no cover
|
|
return None
|
|
|
|
return HtmlTable.from_html_text(text_as_html)
|
|
|
|
def _iter_text_and_html_table_chunks(self) -> Iterator[TableChunk]:
|
|
"""Split table into chunks where HTML corresponds exactly to text.
|
|
|
|
`.metadata.text_as_html` for each chunk is a parsable `<table>` HTML fragment.
|
|
"""
|
|
if (html_table := self._html_table) is None: # pragma: no cover
|
|
raise ValueError("this method is undefined for a table having no .text_as_html")
|
|
|
|
is_continuation = False
|
|
|
|
for text, html in _TableSplitter.iter_subtables(html_table, self._opts):
|
|
metadata = self._metadata
|
|
metadata.text_as_html = html
|
|
# -- second and later chunks get `.metadata.is_continuation = True` --
|
|
metadata.is_continuation = is_continuation or None
|
|
is_continuation = True
|
|
|
|
yield TableChunk(text=text, metadata=metadata)
|
|
|
|
def _iter_text_only_table_chunks(self) -> Iterator[TableChunk]:
|
|
"""Split oversized text-only table (no text-as-html) into chunks."""
|
|
text_remainder = self._text_with_overlap
|
|
split = self._opts.split
|
|
is_continuation = False
|
|
|
|
while text_remainder:
|
|
# -- split off the next chunk-worth of characters into a TableChunk --
|
|
chunk_text, text_remainder = split(text_remainder)
|
|
metadata = self._metadata
|
|
# -- second and later chunks get `.metadata.is_continuation = True` --
|
|
metadata.is_continuation = is_continuation or None
|
|
is_continuation = True
|
|
|
|
yield TableChunk(text=chunk_text, metadata=metadata)
|
|
|
|
@property
|
|
def _metadata(self) -> ElementMetadata:
|
|
"""The base `.metadata` value for chunks formed from this pre-chunk.
|
|
|
|
The term "base" here means that other metadata fields will be added, depending on the
|
|
chunk. In particular, `.metadata.text_as_html` will be different for each text-split chunk
|
|
and `.metadata.is_continuation` must be added for second-and-later text-split chunks.
|
|
|
|
Note this is a fresh copy of the metadata on each call since it will need to be mutated
|
|
differently for each chunk formed from this pre-chunk.
|
|
"""
|
|
CS = ConsolidationStrategy
|
|
metadata = copy.deepcopy(self._table.metadata)
|
|
|
|
# -- drop metadata fields not appropriate for chunks, in particular
|
|
# -- parent_id's will not reliably point to an existing element
|
|
drop_field_names = [
|
|
field_name
|
|
for field_name, strategy in CS.field_consolidation_strategies().items()
|
|
if strategy is CS.DROP
|
|
]
|
|
for field_name in drop_field_names:
|
|
setattr(metadata, field_name, None)
|
|
|
|
if self._opts.include_orig_elements:
|
|
metadata.orig_elements = self._orig_elements
|
|
return metadata
|
|
|
|
@lazyproperty
|
|
def _orig_elements(self) -> list[Element]:
|
|
"""The `.metadata.orig_elements` value for chunks formed from this pre-chunk.
|
|
|
|
Note this is not just the `Table` element, it must be adjusted to strip out any
|
|
`.metadata.orig_elements` value it may have when it is itself a chunk and not a direct
|
|
product of partitioning.
|
|
"""
|
|
# -- make a copy because we're going to mutate the `Table` element and it doesn't belong to
|
|
# -- us (the user may have downstream purposes for it).
|
|
orig_table = copy.deepcopy(self._table)
|
|
# -- prevent recursive .orig_elements when `Table` element is a chunk --
|
|
orig_table.metadata.orig_elements = None
|
|
return [orig_table]
|
|
|
|
@lazyproperty
|
|
def _table_text(self) -> str:
|
|
"""The text in this table, not including any overlap-prefix or extra whitespace."""
|
|
return " ".join(self._table.text.split())
|
|
|
|
@lazyproperty
|
|
def _text_with_overlap(self) -> str:
|
|
"""The text for this chunk, including the overlap-prefix when present."""
|
|
overlap_prefix = self._overlap_prefix
|
|
table_text = self._table.text.strip()
|
|
# -- use row-separator between overlap and table-text --
|
|
return overlap_prefix + "\n" + table_text if overlap_prefix else table_text
|
|
|
|
|
|
class TextPreChunk:
|
|
"""A sequence of elements that belong to the same semantic unit within a document.
|
|
|
|
The name "section" derives from the idea of a document-section, a heading followed by the
|
|
paragraphs "under" that heading. That structure is not found in all documents and actual section
|
|
content can vary, but that's the concept.
|
|
|
|
This object is purposely immutable.
|
|
"""
|
|
|
|
def __init__(
|
|
self, elements: Iterable[Element], overlap_prefix: str, opts: ChunkingOptions
|
|
) -> None:
|
|
self._elements = list(elements)
|
|
self._overlap_prefix = overlap_prefix
|
|
self._opts = opts
|
|
|
|
def __eq__(self, other: Any) -> bool:
|
|
if not isinstance(other, TextPreChunk):
|
|
return False
|
|
return self._overlap_prefix == other._overlap_prefix and self._elements == other._elements
|
|
|
|
def can_combine(self, pre_chunk: TextPreChunk) -> bool:
|
|
"""True when `pre_chunk` can be combined with this one without exceeding size limits."""
|
|
if len(self._text) >= self._opts.combine_text_under_n_chars:
|
|
return False
|
|
# -- avoid duplicating length computations by doing a trial-combine which is just as
|
|
# -- efficient and definitely more robust than hoping two different computations of combined
|
|
# -- length continue to get the same answer as the code evolves. Only possible because
|
|
# -- `.combine()` is non-mutating.
|
|
combined_len = len(self.combine(pre_chunk)._text)
|
|
|
|
return combined_len <= self._opts.hard_max
|
|
|
|
def combine(self, other_pre_chunk: TextPreChunk) -> TextPreChunk:
|
|
"""Return new `TextPreChunk` that combines this and `other_pre_chunk`."""
|
|
# -- combined pre-chunk gets the overlap-prefix of the first pre-chunk. The second overlap
|
|
# -- is automatically incorporated at the end of the first chunk, where it originated.
|
|
return TextPreChunk(
|
|
self._elements + other_pre_chunk._elements,
|
|
overlap_prefix=self._overlap_prefix,
|
|
opts=self._opts,
|
|
)
|
|
|
|
def iter_chunks(self) -> Iterator[CompositeElement]:
|
|
"""Split this pre-chunk into one or more `CompositeElement` objects maxlen or smaller."""
|
|
# -- a pre-chunk containing no text (maybe only a PageBreak element for example) does not
|
|
# -- generate any chunks.
|
|
if not self._text:
|
|
return
|
|
|
|
split = self._opts.split
|
|
|
|
# -- emit first chunk --
|
|
s, remainder = split(self._text)
|
|
yield CompositeElement(text=s, metadata=self._consolidated_metadata)
|
|
|
|
# -- an oversized pre-chunk will have a remainder, split that up into additional chunks.
|
|
# -- Note these get continuation_metadata which includes is_continuation=True.
|
|
while remainder:
|
|
s, remainder = split(remainder)
|
|
yield CompositeElement(text=s, metadata=self._continuation_metadata)
|
|
|
|
@lazyproperty
|
|
def overlap_tail(self) -> str:
|
|
"""The portion of this chunk's text to be repeated as a prefix in the next chunk.
|
|
|
|
This value is the empty-string ("") when either the `.overlap` length option is `0` or
|
|
`.overlap_all` is `False`. When there is a text value, it is stripped of both leading and
|
|
trailing whitespace.
|
|
"""
|
|
overlap = self._opts.inter_chunk_overlap
|
|
return self._text[-overlap:].strip() if overlap else ""
|
|
|
|
@lazyproperty
|
|
def _all_metadata_values(self) -> dict[str, list[Any]]:
|
|
"""Collection of all populated metadata values across elements.
|
|
|
|
The resulting dict has one key for each `ElementMetadata` field that had a non-None value in
|
|
at least one of the elements in this pre-chunk. The value of that key is a list of all those
|
|
populated values, in element order, for example:
|
|
|
|
{
|
|
"filename": ["sample.docx", "sample.docx"],
|
|
"languages": [["lat"], ["lat", "eng"]]
|
|
...
|
|
}
|
|
|
|
This preprocessing step provides the input for a specified consolidation strategy that will
|
|
resolve the list of values for each field to a single consolidated value.
|
|
"""
|
|
|
|
def iter_populated_fields(metadata: ElementMetadata) -> Iterator[tuple[str, Any]]:
|
|
"""(field_name, value) pair for each non-None field in single `ElementMetadata`."""
|
|
return (
|
|
(field_name, value)
|
|
for field_name, value in metadata.known_fields.items()
|
|
if value is not None
|
|
)
|
|
|
|
field_values: DefaultDict[str, list[Any]] = collections.defaultdict(list)
|
|
|
|
# -- collect all non-None field values in a list for each field, in element-order --
|
|
for e in self._elements:
|
|
for field_name, value in iter_populated_fields(e.metadata):
|
|
field_values[field_name].append(value)
|
|
|
|
return dict(field_values)
|
|
|
|
@lazyproperty
|
|
def _consolidated_metadata(self) -> ElementMetadata:
|
|
"""Metadata applicable to this pre-chunk as a single chunk.
|
|
|
|
Formed by applying consolidation rules to all metadata fields across the elements of this
|
|
pre-chunk.
|
|
|
|
For the sake of consistency, the same rules are applied (for example, for dropping values)
|
|
to a single-element pre-chunk too, even though metadata for such a pre-chunk is already
|
|
"consolidated".
|
|
"""
|
|
consolidated_metadata = ElementMetadata(**self._meta_kwargs)
|
|
if self._opts.include_orig_elements:
|
|
consolidated_metadata.orig_elements = self._orig_elements
|
|
return consolidated_metadata
|
|
|
|
@lazyproperty
|
|
def _continuation_metadata(self) -> ElementMetadata:
|
|
"""Metadata applicable to the second and later text-split chunks of the pre-chunk.
|
|
|
|
The same metadata as the first text-split chunk but includes `.is_continuation = True`.
|
|
Unused for non-oversized pre-chunks since those are not subject to text-splitting.
|
|
"""
|
|
# -- we need to make a copy, otherwise adding a field would also change metadata value
|
|
# -- already assigned to another chunk (e.g. the first text-split chunk). Deep-copy is not
|
|
# -- required though since we're not changing any collection fields.
|
|
continuation_metadata = copy.copy(self._consolidated_metadata)
|
|
continuation_metadata.is_continuation = True
|
|
return continuation_metadata
|
|
|
|
def _iter_text_segments(self) -> Iterator[str]:
|
|
"""Generate overlap text and each element text segment in order.
|
|
|
|
Empty text segments are not included.
|
|
"""
|
|
if self._overlap_prefix:
|
|
yield self._overlap_prefix
|
|
for e in self._elements:
|
|
if not e.text:
|
|
continue
|
|
yield e.text
|
|
|
|
@lazyproperty
|
|
def _meta_kwargs(self) -> dict[str, Any]:
|
|
"""The consolidated metadata values as a dict suitable for constructing ElementMetadata.
|
|
|
|
This is where consolidation strategies are actually applied. The output is suitable for use
|
|
in constructing an `ElementMetadata` object like `ElementMetadata(**self._meta_kwargs)`.
|
|
"""
|
|
CS = ConsolidationStrategy
|
|
field_consolidation_strategies = ConsolidationStrategy.field_consolidation_strategies()
|
|
|
|
def iter_kwarg_pairs() -> Iterator[tuple[str, Any]]:
|
|
"""Generate (field-name, value) pairs for each field in consolidated metadata."""
|
|
for field_name, values in self._all_metadata_values.items():
|
|
strategy = field_consolidation_strategies.get(field_name)
|
|
if strategy is CS.FIRST:
|
|
yield field_name, values[0]
|
|
# -- concatenate lists from each element that had one, in order --
|
|
elif strategy is CS.LIST_CONCATENATE:
|
|
yield field_name, sum(values, cast("list[Any]", []))
|
|
# -- union lists from each element, preserving order of appearance --
|
|
elif strategy is CS.LIST_UNIQUE:
|
|
# -- Python 3.7+ maintains dict insertion order --
|
|
ordered_unique_keys = {key: None for val_list in values for key in val_list}
|
|
yield field_name, list(ordered_unique_keys.keys())
|
|
elif strategy is CS.STRING_CONCATENATE:
|
|
yield field_name, " ".join(val.strip() for val in values)
|
|
elif strategy is CS.DROP:
|
|
continue
|
|
else: # pragma: no cover
|
|
# -- not likely to hit this since we have a test in `text_elements.py` that
|
|
# -- ensures every ElementMetadata fields has an assigned strategy.
|
|
raise NotImplementedError(
|
|
f"metadata field {repr(field_name)} has no defined consolidation strategy"
|
|
)
|
|
|
|
return dict(iter_kwarg_pairs())
|
|
|
|
@lazyproperty
|
|
def _orig_elements(self) -> list[Element]:
|
|
"""The `.metadata.orig_elements` value for chunks formed from this pre-chunk."""
|
|
|
|
def iter_orig_elements():
|
|
for e in self._elements:
|
|
if e.metadata.orig_elements is None:
|
|
yield e
|
|
continue
|
|
# -- make copy of any element we're going to mutate because these elements don't
|
|
# -- belong to us (the user may have downstream purposes for them).
|
|
orig_element = copy.copy(e)
|
|
# -- prevent recursive .orig_elements when element is a chunk (has orig-elements of
|
|
# -- its own)
|
|
orig_element.metadata.orig_elements = None
|
|
yield orig_element
|
|
|
|
return list(iter_orig_elements())
|
|
|
|
@lazyproperty
|
|
def _text(self) -> str:
|
|
"""The concatenated text of all elements in this pre-chunk.
|
|
|
|
Each element-text is separated from the next by a blank line ("\n\n").
|
|
"""
|
|
text_separator = self._opts.text_separator
|
|
return text_separator.join(self._iter_text_segments())
|
|
|
|
|
|
# ================================================================================================
|
|
# PRE-CHUNK SPLITTERS
|
|
# ================================================================================================
|
|
|
|
|
|
class _TableSplitter:
|
|
"""Produces (text, html) pairs for a `<table>` HtmlElement.
|
|
|
|
Each chunk contains a whole number of rows whenever possible. An oversized row is split on an
|
|
even cell boundary and a single cell that is by itself too big to fit in the chunking window
|
|
is divided by text-splitting.
|
|
|
|
The returned `html` value is always a parseable HTML `<table>` subtree.
|
|
"""
|
|
|
|
def __init__(self, table_element: HtmlTable, opts: ChunkingOptions):
|
|
self._table_element = table_element
|
|
self._opts = opts
|
|
|
|
@classmethod
|
|
def iter_subtables(
|
|
cls, table_element: HtmlTable, opts: ChunkingOptions
|
|
) -> Iterator[TextAndHtml]:
|
|
"""Generate (text, html) pair for each split of this table pre-chunk.
|
|
|
|
Each split is on an even row boundary whenever possible, falling back to even cell and even
|
|
word boundaries when a row or cell is by itself oversized, respectively.
|
|
"""
|
|
return cls(table_element, opts)._iter_subtables()
|
|
|
|
def _iter_subtables(self) -> Iterator[TextAndHtml]:
|
|
"""Generate (text, html) pairs containing as many whole rows as will fit in window.
|
|
|
|
Falls back to splitting rows into whole cells when a single row is by itself too big to
|
|
fit in the chunking window.
|
|
"""
|
|
accum = _RowAccumulator(maxlen=self._opts.hard_max)
|
|
|
|
for row in self._table_element.iter_rows():
|
|
# -- if row won't fit, any WIP chunk is done, send it on its way --
|
|
if not accum.will_fit(row):
|
|
yield from accum.flush()
|
|
# -- if row fits, add it to accumulator --
|
|
if accum.will_fit(row):
|
|
accum.add_row(row)
|
|
else: # -- otherwise, single row is bigger than chunking window --
|
|
yield from self._iter_row_splits(row)
|
|
|
|
yield from accum.flush()
|
|
|
|
def _iter_row_splits(self, row: HtmlRow) -> Iterator[TextAndHtml]:
|
|
"""Split oversized row into (text, html) pairs containing as many cells as will fit."""
|
|
accum = _CellAccumulator(maxlen=self._opts.hard_max)
|
|
|
|
for cell in row.iter_cells():
|
|
# -- if cell won't fit, flush and check again --
|
|
if not accum.will_fit(cell):
|
|
yield from accum.flush()
|
|
# -- if cell fits, add it to accumulator --
|
|
if accum.will_fit(cell):
|
|
accum.add_cell(cell)
|
|
else: # -- otherwise, single cell is bigger than chunking window --
|
|
yield from self._iter_cell_splits(cell)
|
|
|
|
yield from accum.flush()
|
|
|
|
def _iter_cell_splits(self, cell: HtmlCell) -> Iterator[TextAndHtml]:
|
|
"""Split a single oversized cell into sub-sub-sub-table HTML fragments."""
|
|
# -- 33 is len("<table><tr><td></td></tr></table>"), HTML overhead beyond text content --
|
|
opts = ChunkingOptions(max_characters=(self._opts.hard_max - 33))
|
|
split = _TextSplitter(opts)
|
|
|
|
text, remainder = split(cell.text)
|
|
yield text, f"<table><tr><td>{text}</td></tr></table>"
|
|
|
|
# -- an oversized cell will have a remainder, split that up into additional chunks.
|
|
while remainder:
|
|
text, remainder = split(remainder)
|
|
yield text, f"<table><tr><td>{text}</td></tr></table>"
|
|
|
|
|
|
class _TextSplitter:
|
|
"""Provides a text-splitting function configured on construction.
|
|
|
|
Text is split on the best-available separator, falling-back from the preferred separator
|
|
through a sequence of alternate separators.
|
|
|
|
- The separator is removed by splitting so only whitespace strings are suitable separators.
|
|
- A "blank-line" ("\n\n") is unlikely to occur in an element as it would have been used as an
|
|
element boundary during partitioning.
|
|
|
|
This is a *callable* object. Constructing it essentially produces a function:
|
|
|
|
split = _TextSplitter(opts)
|
|
fragment, remainder = split(s)
|
|
|
|
This allows it to be configured with length-options etc. on construction and used throughout a
|
|
chunking operation on a given element-stream.
|
|
"""
|
|
|
|
def __init__(self, opts: ChunkingOptions):
|
|
self._opts = opts
|
|
|
|
def __call__(self, s: str) -> tuple[str, str]:
|
|
"""Return pair of strings split from `s` on the best match of configured patterns.
|
|
|
|
The first string is the split, the second is the remainder of the string. The split string
|
|
will never be longer than `maxlen`. The separators are tried in order until a match is
|
|
found. The last separator is "" which matches between any two characters so there will
|
|
always be a split.
|
|
|
|
The separator is removed and does not appear in the split or remainder.
|
|
|
|
An `s` that is already less than the maximum length is returned unchanged with no remainder.
|
|
This allows this function to be called repeatedly with the remainder until it is consumed
|
|
and returns a remainder of "".
|
|
"""
|
|
maxlen = self._opts.hard_max
|
|
|
|
if len(s) <= maxlen:
|
|
return s, ""
|
|
|
|
for p, sep_len in self._patterns:
|
|
# -- length of separator must be added to include that separator when it happens to be
|
|
# -- located exactly at maxlen. Otherwise the search-from-end regex won't find it.
|
|
fragment, remainder = self._split_from_maxlen(p, sep_len, s)
|
|
if (
|
|
# -- no available split with this separator --
|
|
not fragment
|
|
# -- split did not progress, consuming part of the string --
|
|
or len(remainder) >= len(s)
|
|
):
|
|
continue
|
|
return fragment.rstrip(), remainder.lstrip()
|
|
|
|
# -- the terminal "" pattern is not actually executed via regex since its implementation is
|
|
# -- trivial and provides a hard back-stop here in this method. No separator is used between
|
|
# -- tail and remainder on arb-char split.
|
|
return s[:maxlen].rstrip(), s[maxlen - self._opts.overlap :].lstrip()
|
|
|
|
@lazyproperty
|
|
def _patterns(self) -> tuple[tuple[regex.Pattern[str], int], ...]:
|
|
"""Sequence of (pattern, len) pairs to match against.
|
|
|
|
Patterns appear in order of preference, those following are "fall-back" patterns to be used
|
|
if no match of a prior pattern is found.
|
|
|
|
NOTE these regexes search *from the end of the string*, which is what the "(?r)" bit
|
|
specifies. This is much more efficient than starting at the beginning of the string which
|
|
could result in hundreds of matches before the desired one.
|
|
"""
|
|
separators = self._opts.text_splitting_separators
|
|
return tuple((regex.compile(f"(?r){sep}"), len(sep)) for sep in separators)
|
|
|
|
def _split_from_maxlen(
|
|
self, pattern: regex.Pattern[str], sep_len: int, s: str
|
|
) -> tuple[str, str]:
|
|
"""Return (split, remainder) pair split from `s` on the right-most match before `maxlen`.
|
|
|
|
Returns `"", s` if no suitable match was found. Also returns `"", s` if splitting on this
|
|
separator produces a split shorter than the required overlap (which would produce an
|
|
infinite loop).
|
|
|
|
`split` will never be longer than `maxlen` and there is no longer split available using
|
|
`pattern`.
|
|
|
|
The separator is removed and does not appear in either the split or remainder.
|
|
"""
|
|
maxlen, overlap = self._opts.hard_max, self._opts.overlap
|
|
|
|
# -- A split not longer than overlap will not progress (infinite loop). On the right side,
|
|
# -- need to extend search range to include a separator located exactly at maxlen.
|
|
match = pattern.search(s, pos=overlap + 1, endpos=maxlen + sep_len)
|
|
if match is None:
|
|
return "", s
|
|
|
|
# -- characterize match location
|
|
match_start, match_end = match.span()
|
|
# -- matched separator is replaced by single-space in overlap string --
|
|
separator = " "
|
|
|
|
# -- in multi-space situation, fragment may have trailing whitespace because match is from
|
|
# -- right to left
|
|
fragment = s[:match_start].rstrip()
|
|
# -- remainder can have leading space when match is on "\n" followed by spaces --
|
|
raw_remainder = s[match_end:].lstrip()
|
|
|
|
if overlap <= len(separator):
|
|
return fragment, raw_remainder
|
|
|
|
# -- compute overlap --
|
|
tail_len = overlap - len(separator)
|
|
tail = fragment[-tail_len:].lstrip()
|
|
overlapped_remainder = tail + separator + raw_remainder
|
|
return fragment, overlapped_remainder
|
|
|
|
|
|
class _CellAccumulator:
|
|
"""Incrementally build `<table>` fragment cell-by-cell to maximally fill chunking window.
|
|
|
|
Accumulate cells until chunking window is filled, then generate the text and HTML for the
|
|
subtable composed of all those rows that fit in the window.
|
|
"""
|
|
|
|
def __init__(self, maxlen: int):
|
|
self._maxlen = maxlen
|
|
self._cells: list[HtmlCell] = []
|
|
|
|
def add_cell(self, cell: HtmlCell) -> None:
|
|
"""Add `cell` to this accumulation. Caller is responsible for ensuring it will fit."""
|
|
self._cells.append(cell)
|
|
|
|
def flush(self) -> Iterator[TextAndHtml]:
|
|
"""Generate zero-or-one (text, html) pairs for accumulated sub-sub-table."""
|
|
if not self._cells:
|
|
return
|
|
text = " ".join(self._iter_cell_texts())
|
|
tds_str = "".join(c.html for c in self._cells)
|
|
html = f"<table><tr>{tds_str}</tr></table>"
|
|
self._cells.clear()
|
|
yield text, html
|
|
|
|
def will_fit(self, cell: HtmlCell) -> bool:
|
|
"""True when `cell` will fit within remaining space left by accummulated cells."""
|
|
return self._remaining_space >= len(cell.html)
|
|
|
|
def _iter_cell_texts(self) -> Iterator[str]:
|
|
"""Generate contents of each accumulated cell as a separate string.
|
|
|
|
A cell that is empty or contains only whitespace does not generate a string.
|
|
"""
|
|
for cell in self._cells:
|
|
if not (text := cell.text):
|
|
continue
|
|
yield text
|
|
|
|
@property
|
|
def _remaining_space(self) -> int:
|
|
"""Number of characters remaining when accumulated cells are formed into HTML."""
|
|
# -- 24 is `len("<table><tr></tr></table>")`, the overhead in addition to `<td>`
|
|
# -- HTML fragments
|
|
return self._maxlen - 24 - sum(len(c.html) for c in self._cells)
|
|
|
|
|
|
class _RowAccumulator:
|
|
"""Maybe `SubtableAccumulator`.
|
|
|
|
Accumulate rows until chunking window is filled, then generate the text and HTML for the
|
|
subtable composed of all those rows that fit in the window.
|
|
"""
|
|
|
|
def __init__(self, maxlen: int):
|
|
self._maxlen = maxlen
|
|
self._rows: list[HtmlRow] = []
|
|
|
|
def add_row(self, row: HtmlRow) -> None:
|
|
"""Add `row` to this accumulation. Caller is responsible for ensuring it will fit."""
|
|
self._rows.append(row)
|
|
|
|
def flush(self) -> Iterator[TextAndHtml]:
|
|
"""Generate zero-or-one (text, html) pairs for accumulated sub-table."""
|
|
if not self._rows:
|
|
return
|
|
text = " ".join(self._iter_cell_texts())
|
|
trs_str = "".join(r.html for r in self._rows)
|
|
html = f"<table>{trs_str}</table>"
|
|
self._rows.clear()
|
|
yield text, html
|
|
|
|
def will_fit(self, row: HtmlRow) -> bool:
|
|
"""True when `row` will fit within remaining space left by accummulated rows."""
|
|
return self._remaining_space >= len(row.html)
|
|
|
|
def _iter_cell_texts(self) -> Iterator[str]:
|
|
"""Generate contents of each row cell as a separate string.
|
|
|
|
A cell that is empty or contains only whitespace does not generate a string.
|
|
"""
|
|
for r in self._rows:
|
|
yield from r.iter_cell_texts()
|
|
|
|
@property
|
|
def _remaining_space(self) -> int:
|
|
"""Number of characters remaining when accumulated rows are formed into HTML."""
|
|
# -- 15 is `len("<table></table>")`, the overhead in addition to `<tr>` HTML fragments --
|
|
return self._maxlen - 15 - sum(len(r.html) for r in self._rows)
|
|
|
|
|
|
# ================================================================================================
|
|
# PRE-CHUNK COMBINER
|
|
# ================================================================================================
|
|
|
|
|
|
class PreChunkCombiner:
|
|
"""Filters pre-chunk stream to combine small pre-chunks where possible."""
|
|
|
|
def __init__(self, pre_chunks: Iterable[PreChunk], opts: ChunkingOptions):
|
|
self._pre_chunks = pre_chunks
|
|
self._opts = opts
|
|
|
|
def iter_combined_pre_chunks(self) -> Iterator[PreChunk]:
|
|
"""Generate pre-chunk objects, combining TextPreChunk objects when they'll fit in window."""
|
|
accum = TextPreChunkAccumulator(self._opts)
|
|
|
|
for pre_chunk in self._pre_chunks:
|
|
# -- a table pre-chunk is never combined --
|
|
if isinstance(pre_chunk, TablePreChunk):
|
|
yield from accum.flush()
|
|
yield pre_chunk
|
|
continue
|
|
|
|
# -- finish accumulating pre-chunk when it's full --
|
|
if not accum.will_fit(pre_chunk):
|
|
yield from accum.flush()
|
|
|
|
accum.add_pre_chunk(pre_chunk)
|
|
|
|
yield from accum.flush()
|
|
|
|
|
|
class TextPreChunkAccumulator:
|
|
"""Accumulates, measures, and combines text pre-chunks.
|
|
|
|
Used for combining pre-chunks for chunking strategies like "by-title" that can potentially
|
|
produce undersized chunks and offer the `combine_text_under_n_chars` option. Note that only
|
|
sequential `TextPreChunk` objects can be combined. A `TablePreChunk` is never combined with
|
|
another pre-chunk.
|
|
|
|
Provides `.add_pre_chunk()` allowing a pre-chunk to be added to the chunk and provides
|
|
monitoring properties `.remaining_space` and `.text_length` suitable for deciding whether to add
|
|
another pre-chunk.
|
|
|
|
`.flush()` is used to combine the accumulated pre-chunks into a single `TextPreChunk` object.
|
|
This method returns an interator that generates zero-or-one `TextPreChunk` objects and is used
|
|
like so:
|
|
|
|
yield from accum.flush()
|
|
|
|
If no pre-chunks have been accumulated, no `TextPreChunk` is generated. Flushing the builder
|
|
clears the pre-chunks it contains so it is ready to accept the next text-pre-chunk.
|
|
"""
|
|
|
|
def __init__(self, opts: ChunkingOptions) -> None:
|
|
self._opts = opts
|
|
self._pre_chunk: TextPreChunk | None = None
|
|
|
|
def add_pre_chunk(self, pre_chunk: TextPreChunk) -> None:
|
|
"""Add a pre-chunk to the accumulator for possible combination with next pre-chunk."""
|
|
self._pre_chunk = (
|
|
pre_chunk if self._pre_chunk is None else self._pre_chunk.combine(pre_chunk)
|
|
)
|
|
|
|
def flush(self) -> Iterator[TextPreChunk]:
|
|
"""Generate accumulated pre-chunk as a single combined pre-chunk.
|
|
|
|
Does not generate a pre-chunk when none has been accumulated.
|
|
"""
|
|
# -- nothing to do if no pre-chunk has been accumulated --
|
|
if not self._pre_chunk:
|
|
return
|
|
# -- otherwise generate the combined pre-chunk --
|
|
yield self._pre_chunk
|
|
# -- and reset the accumulator (to empty) --
|
|
self._pre_chunk = None
|
|
|
|
def will_fit(self, pre_chunk: TextPreChunk) -> bool:
|
|
"""True when there is room for `pre_chunk` in accumulator.
|
|
|
|
An empty accumulator always has room. Otherwise there is only room when `pre_chunk` can be
|
|
combined with any other pre-chunks in the accumulator without exceeding the combination
|
|
limits specified for the chunking run.
|
|
"""
|
|
# -- an empty accumulator always has room --
|
|
if self._pre_chunk is None:
|
|
return True
|
|
|
|
return self._pre_chunk.can_combine(pre_chunk)
|
|
|
|
|
|
# ================================================================================================
|
|
# CHUNK BOUNDARY PREDICATES
|
|
# ------------------------------------------------------------------------------------------------
|
|
# A *boundary predicate* is a function that takes an element and returns True when the element
|
|
# represents the start of a new semantic boundary (such as section or page) to be respected in
|
|
# chunking.
|
|
#
|
|
# Some of the functions below *are* a boundary predicate and others *construct* a boundary
|
|
# predicate.
|
|
#
|
|
# These can be mixed and matched to produce different chunking behaviors like "by_title" or left
|
|
# out altogether to produce "by_element" behavior.
|
|
#
|
|
# The effective lifetime of the function that produce a predicate (rather than directly being one)
|
|
# is limited to a single element-stream because these retain state (e.g. current page number) to
|
|
# determine when a semantic boundary has been crossed.
|
|
# ================================================================================================
|
|
|
|
|
|
def is_on_next_page() -> BoundaryPredicate:
|
|
"""Not a predicate itself, calling this returns a predicate that triggers on each new page.
|
|
|
|
The lifetime of the returned callable cannot extend beyond a single element-stream because it
|
|
stores current state (current page-number) that is particular to that element stream.
|
|
|
|
The returned predicate tracks the "current" page-number, starting at 1. An element with a
|
|
greater page number returns True, indicating the element starts a new page boundary, and
|
|
updates the enclosed page-number ready for the next transition.
|
|
|
|
An element with `page_number == None` or a page-number lower than the stored value is ignored
|
|
and returns False.
|
|
"""
|
|
current_page_number: int = 1
|
|
is_first: bool = True
|
|
|
|
def page_number_incremented(element: Element) -> bool:
|
|
nonlocal current_page_number, is_first
|
|
|
|
page_number = element.metadata.page_number
|
|
|
|
# -- The first element never reports a page break, it starts the first page of the
|
|
# -- document. That page could be numbered (page_number is non-None) or not. If it is not
|
|
# -- numbered we assign it page-number 1.
|
|
if is_first:
|
|
current_page_number = page_number or 1
|
|
is_first = False
|
|
return False
|
|
|
|
# -- An element with a `None` page-number is assumed to continue the current page. It never
|
|
# -- updates the current-page-number because once set, the current-page-number is "sticky"
|
|
# -- until replaced by a different explicit page-number.
|
|
if page_number is None:
|
|
return False
|
|
|
|
if page_number == current_page_number:
|
|
return False
|
|
|
|
# -- it's possible for a page-number to decrease. We don't expect that, but if it happens
|
|
# -- we consider it a page-break.
|
|
current_page_number = page_number
|
|
return True
|
|
|
|
return page_number_incremented
|
|
|
|
|
|
def is_title(element: Element) -> bool:
|
|
"""True when `element` is a `Title` element, False otherwise."""
|
|
return isinstance(element, Title)
|