fix: Bring in fix from custom nodes (#8539)

* Bring in fix from custom nodes

* Add to_dict function and test

* reno

* Fix pylint

haystack/components/preprocessors/nltk_document_splitter.py

@@ -5,11 +5,13 @@
 import re
 from copy import deepcopy
 from pathlib import Path
-from typing import Any, Dict, List, Literal, Tuple
+from typing import Any, Callable, Dict, List, Literal, Optional, Tuple
 
 from haystack import Document, component, logging
 from haystack.components.preprocessors.document_splitter import DocumentSplitter
+from haystack.core.serialization import default_to_dict
 from haystack.lazy_imports import LazyImport
+from haystack.utils import serialize_callable
 
 with LazyImport("Run 'pip install nltk'") as nltk_imports:
     import nltk
@@ -23,7 +25,7 @@
 
 @component
 class NLTKDocumentSplitter(DocumentSplitter):
-    def __init__(
+    def __init__(  # pylint: disable=too-many-positional-arguments
         self,
         split_by: Literal["word", "sentence", "page", "passage", "function"] = "word",
         split_length: int = 200,
@@ -33,6 +35,7 @@ def __init__(
         language: Language = "en",
         use_split_rules: bool = True,
         extend_abbreviations: bool = True,
+        splitting_function: Optional[Callable[[str], List[str]]] = None,
     ):
         """
         Splits your documents using NLTK to respect sentence boundaries.
@@ -53,10 +56,17 @@ def __init__(
         :param extend_abbreviations: Choose whether to extend NLTK's PunktTokenizer abbreviations with a list
             of curated abbreviations, if available.
             This is currently supported for English ("en") and German ("de").
+        :param splitting_function: Necessary when `split_by` is set to "function".
+            This is a function which must accept a single `str` as input and return a `list` of `str` as output,
+            representing the chunks after splitting.
         """
 
         super(NLTKDocumentSplitter, self).__init__(
-            split_by=split_by, split_length=split_length, split_overlap=split_overlap, split_threshold=split_threshold
+            split_by=split_by,
+            split_length=split_length,
+            split_overlap=split_overlap,
+            split_threshold=split_threshold,
+            splitting_function=splitting_function,
         )
         nltk_imports.check()
         if respect_sentence_boundary and split_by != "word":
@@ -66,6 +76,8 @@ def __init__(
             )
             respect_sentence_boundary = False
         self.respect_sentence_boundary = respect_sentence_boundary
+        self.use_split_rules = use_split_rules
+        self.extend_abbreviations = extend_abbreviations
         self.sentence_splitter = SentenceSplitter(
             language=language,
             use_split_rules=use_split_rules,
@@ -100,9 +112,11 @@ def _split_into_units(
         elif split_by == "word":
             self.split_at = " "
             units = text.split(self.split_at)
+        elif split_by == "function" and self.splitting_function is not None:
+            return self.splitting_function(text)
         else:
             raise NotImplementedError(
-                "DocumentSplitter only supports 'word', 'sentence', 'page' or 'passage' split_by options."
+                "DocumentSplitter only supports 'function', 'page', 'passage', 'sentence' or 'word' split_by options."
             )
 
         # Add the delimiter back to all units except the last one
@@ -138,6 +152,9 @@ def run(self, documents: List[Document]) -> Dict[str, List[Document]]:
                 raise ValueError(
                     f"DocumentSplitter only works with text documents but content for document ID {doc.id} is None."
                 )
+            if doc.content == "":
+                logger.warning("Document ID {doc_id} has an empty content. Skipping this document.", doc_id=doc.id)
+                continue
 
             if self.respect_sentence_boundary:
                 units = self._split_into_units(doc.content, "sentence")
@@ -159,6 +176,25 @@ def run(self, documents: List[Document]) -> Dict[str, List[Document]]:
             )
         return {"documents": split_docs}
 
+    def to_dict(self) -> Dict[str, Any]:
+        """
+        Serializes the component to a dictionary.
+        """
+        serialized = default_to_dict(
+            self,
+            split_by=self.split_by,
+            split_length=self.split_length,
+            split_overlap=self.split_overlap,
+            split_threshold=self.split_threshold,
+            respect_sentence_boundary=self.respect_sentence_boundary,
+            language=self.language,
+            use_split_rules=self.use_split_rules,
+            extend_abbreviations=self.extend_abbreviations,
+        )
+        if self.splitting_function:
+            serialized["init_parameters"]["splitting_function"] = serialize_callable(self.splitting_function)
+        return serialized
+
     @staticmethod
     def _number_of_sentences_to_keep(sentences: List[str], split_length: int, split_overlap: int) -> int:
         """
@@ -175,7 +211,8 @@ def _number_of_sentences_to_keep(sentences: List[str], split_length: int, split_
 
         num_sentences_to_keep = 0
         num_words = 0
-        for sent in reversed(sentences):
+        # Next overlapping Document should not start exactly the same as the previous one, so we skip the first sentence
+        for sent in reversed(sentences[1:]):
             num_words += len(sent.split())
             # If the number of words is larger than the split_length then don't add any more sentences
             if num_words > split_length:

releasenotes/notes/fix-nltk-doc-splitter-d0864dda906c45b0.yaml

@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    For the NLTKDocumentSplitter we are updating how chunks are made when splitting by word and sentence boundary is respected.
+    Namely, to avoid fully subsuming the previous chunk into the next one, we ignore the first sentence from that chunk when calculating sentence overlap.
+    i.e. we want to avoid cases of Doc1 = [s1, s2], Doc2 = [s1, s2, s3].
+
+    Finished adding function support for this component by updating the _split_into_units function and added the splitting_function init parameter.
+
+    Add specific to_dict method to overwrite the underlying one from DocumentSplitter. This is needed to properly save the settings of the component to yaml.

test/components/preprocessors/test_nltk_document_splitter.py

@@ -5,13 +5,18 @@
 from pytest import LogCaptureFixture
 
 from haystack.components.preprocessors.nltk_document_splitter import NLTKDocumentSplitter, SentenceSplitter
+from haystack.utils import deserialize_callable
 
 
 def test_init_warning_message(caplog: LogCaptureFixture) -> None:
     _ = NLTKDocumentSplitter(split_by="page", respect_sentence_boundary=True)
     assert "The 'respect_sentence_boundary' option is only supported for" in caplog.text
 
 
+def custom_split(text):
+    return text.split(".")
+
+
 class TestNLTKDocumentSplitterSplitIntoUnits:
     def test_document_splitter_split_into_units_word(self) -> None:
         document_splitter = NLTKDocumentSplitter(
@@ -87,9 +92,11 @@ class TestNLTKDocumentSplitterNumberOfSentencesToKeep:
     @pytest.mark.parametrize(
         "sentences, expected_num_sentences",
         [
-            (["Moonlight shimmered softly, wolves howled nearby, night enveloped everything."], 0),
-            ([" It was a dark night ..."], 0),
-            ([" The moon was full."], 1),
+            (["The sun set.", "Moonlight shimmered softly, wolves howled nearby, night enveloped everything."], 0),
+            (["The sun set.", "It was a dark night ..."], 0),
+            (["The sun set.", " The moon was full."], 1),
+            (["The sun.", " The moon."], 1),  # Ignores the first sentence
+            (["Sun", "Moon"], 1),  # Ignores the first sentence even if its inclusion would be < split_overlap
         ],
     )
     def test_number_of_sentences_to_keep(self, sentences: List[str], expected_num_sentences: int) -> None:
@@ -304,7 +311,7 @@ def test_run_split_by_word_respect_sentence_boundary_no_repeats(self) -> None:
     def test_run_split_by_word_respect_sentence_boundary_with_split_overlap_and_page_breaks(self) -> None:
         document_splitter = NLTKDocumentSplitter(
             split_by="word",
-            split_length=5,
+            split_length=8,
             split_overlap=1,
             split_threshold=0,
             language="en",
@@ -313,26 +320,60 @@ def test_run_split_by_word_respect_sentence_boundary_with_split_overlap_and_page
             respect_sentence_boundary=True,
         )
 
-        text = "Sentence on page 1.\fSentence on page 2. \fSentence on page 3. \f\f Sentence on page 5."
+        text = (
+            "Sentence on page 1. Another on page 1.\fSentence on page 2. Another on page 2.\f"
+            "Sentence on page 3. Another on page 3.\f\f Sentence on page 5."
+        )
         documents = document_splitter.run(documents=[Document(content=text)])["documents"]
 
-        assert len(documents) == 4
-        assert documents[0].content == "Sentence on page 1.\f"
+        assert len(documents) == 6
+        assert documents[0].content == "Sentence on page 1. Another on page 1.\f"
         assert documents[0].meta["page_number"] == 1
         assert documents[0].meta["split_id"] == 0
         assert documents[0].meta["split_idx_start"] == text.index(documents[0].content)
-        assert documents[1].content == "Sentence on page 1.\fSentence on page 2. \f"
+        assert documents[1].content == "Another on page 1.\fSentence on page 2. "
         assert documents[1].meta["page_number"] == 1
         assert documents[1].meta["split_id"] == 1
         assert documents[1].meta["split_idx_start"] == text.index(documents[1].content)
-        assert documents[2].content == "Sentence on page 2. \fSentence on page 3. \f\f "
+        assert documents[2].content == "Sentence on page 2. Another on page 2.\f"
         assert documents[2].meta["page_number"] == 2
         assert documents[2].meta["split_id"] == 2
         assert documents[2].meta["split_idx_start"] == text.index(documents[2].content)
-        assert documents[3].content == "Sentence on page 3. \f\f Sentence on page 5."
-        assert documents[3].meta["page_number"] == 3
+        assert documents[3].content == "Another on page 2.\fSentence on page 3. "
+        assert documents[3].meta["page_number"] == 2
         assert documents[3].meta["split_id"] == 3
         assert documents[3].meta["split_idx_start"] == text.index(documents[3].content)
+        assert documents[4].content == "Sentence on page 3. Another on page 3.\f\f "
+        assert documents[4].meta["page_number"] == 3
+        assert documents[4].meta["split_id"] == 4
+        assert documents[4].meta["split_idx_start"] == text.index(documents[4].content)
+        assert documents[5].content == "Another on page 3.\f\f Sentence on page 5."
+        assert documents[5].meta["page_number"] == 3
+        assert documents[5].meta["split_id"] == 5
+        assert documents[5].meta["split_idx_start"] == text.index(documents[5].content)
+
+    def test_to_dict(self):
+        splitter = NLTKDocumentSplitter(split_by="word", split_length=10, split_overlap=2, split_threshold=5)
+        serialized = splitter.to_dict()
+
+        assert serialized["type"] == "haystack.components.preprocessors.nltk_document_splitter.NLTKDocumentSplitter"
+        assert serialized["init_parameters"]["split_by"] == "word"
+        assert serialized["init_parameters"]["split_length"] == 10
+        assert serialized["init_parameters"]["split_overlap"] == 2
+        assert serialized["init_parameters"]["split_threshold"] == 5
+        assert serialized["init_parameters"]["language"] == "en"
+        assert serialized["init_parameters"]["use_split_rules"] is True
+        assert serialized["init_parameters"]["extend_abbreviations"] is True
+        assert "splitting_function" not in serialized["init_parameters"]
+
+    def test_to_dict_with_splitting_function(self):
+        splitter = NLTKDocumentSplitter(split_by="function", splitting_function=custom_split)
+        serialized = splitter.to_dict()
+
+        assert serialized["type"] == "haystack.components.preprocessors.nltk_document_splitter.NLTKDocumentSplitter"
+        assert serialized["init_parameters"]["split_by"] == "function"
+        assert "splitting_function" in serialized["init_parameters"]
+        assert callable(deserialize_callable(serialized["init_parameters"]["splitting_function"]))
 
 
 class TestSentenceSplitter: