HTML头部元数据（HTMLHeaderMetadata）

描述和动机

与MarkdownHeaderTextSplitter概念相似，HTMLHeaderTextSplitter是一个“结构感知”的分块器，它在元素级别分割文本，并为每个与给定块“相关”的标题添加元数据。它可以逐个元素返回块，或者合并具有相同元数据的元素，目标是(a)在语义上（或多或少）保持相关文本的分组，以及(b)保留在文档结构中编码的丰富上下文信息。它可以作为分块管道的一部分与其他文本分割器一起使用。

使用示例

1) 使用 HTML 字符串：

%pip install -qU langchain-text-splitters

from langchain_text_splitters import HTMLHeaderTextSplitter
 
html_string = """
<!DOCTYPE html>
<html>
<body>
    <div>
        <h1>Foo</h1>
        <p>Some intro text about Foo.</p>
        <div>
            <h2>Bar main section</h2>
            <p>Some intro text about Bar.</p>
            <h3>Bar subsection 1</h3>
            <p>Some text about the first subtopic of Bar.</p>
            <h3>Bar subsection 2</h3>
            <p>Some text about the second subtopic of Bar.</p>
        </div>
        <div>
            <h2>Baz</h2>
            <p>Some text about Baz</p>
        </div>
        <br>
        <p>Some concluding text about Foo</p>
    </div>
</body>
</html>
"""
 
headers_to_split_on = [
    ("h1", "Header 1"),
    ("h2", "Header 2"),
    ("h3", "Header 3"),
]
 
html_splitter = HTMLHeaderTextSplitter(headers_to_split_on=headers_to_split_on)
html_header_splits = html_splitter.split_text(html_string)
html_header_splits

[Document(page_content='Foo'),
 Document(page_content='Some intro text about Foo.  \nBar main section Bar subsection 1 Bar subsection 2', metadata={'Header 1': 'Foo'}),
 Document(page_content='Some intro text about Bar.', metadata={'Header 1': 'Foo', 'Header 2': 'Bar main section'}),
 Document(page_content='Some text about the first subtopic of Bar.', metadata={'Header 1': 'Foo', 'Header 2': 'Bar main section', 'Header 3': 'Bar subsection 1'}),
 Document(page_content='Some text about the second subtopic of Bar.', metadata={'Header 1': 'Foo', 'Header 2': 'Bar main section', 'Header 3': 'Bar subsection 2'}),
 Document(page_content='Baz', metadata={'Header 1': 'Foo'}),
 Document(page_content='Some text about Baz', metadata={'Header 1': 'Foo', 'Header 2': 'Baz'}),
 Document(page_content='Some concluding text about Foo', metadata={'Header 1': 'Foo'})]

2) 与另一个分割器管道化，HTML 内容从网页 URL 加载：

from langchain_text_splitters import RecursiveCharacterTextSplitter
 
url = "https://plato.stanford.edu/entries/goedel/"
 
headers_to_split_on = [
    ("h1", "Header 1"),
    ("h2", "Header 2"),
    ("h3", "Header 3"),
    ("h4", "Header 4"),
]
 
html_splitter = HTMLHeaderTextSplitter(headers_to_split_on=headers_to_split_on)
 
# for local file use html_splitter.split_text_from_file(<path_to_file>)
html_header_splits = html_splitter.split_text_from_url(url)
 
chunk_size = 500
chunk_overlap = 30
text_splitter = RecursiveCharacterTextSplitter(
    chunk_size=chunk_size, chunk_overlap=chunk_overlap
)
 
# Split
splits = text_splitter.split_documents(html_header_splits)
splits[80:85]

[Document(page_content='We see that Gödel first tried to reduce the consistency problem for analysis to that of arithmetic. This seemed to require a truth definition for arithmetic, which in turn led to paradoxes, such as the Liar paradox (“This sentence is false”) and Berry’s paradox (“The least number not defined by an expression consisting of just fourteen English words”). Gödel then noticed that such paradoxes would not necessarily arise if truth were replaced by provability. But this means that arithmetic truth', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.1 The First Incompleteness Theorem'}),
 Document(page_content='means that arithmetic truth and arithmetic provability are not co-extensive — whence the First Incompleteness Theorem.', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.1 The First Incompleteness Theorem'}),
 Document(page_content='This account of Gödel’s discovery was told to Hao Wang very much after the fact; but in Gödel’s contemporary correspondence with Bernays and Zermelo, essentially the same description of his path to the theorems is given. (See Gödel 2003a and Gödel 2003b respectively.) From those accounts we see that the undefinability of truth in arithmetic, a result credited to Tarski, was likely obtained in some form by Gödel by 1931. But he neither publicized nor published the result; the biases logicians', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.1 The First Incompleteness Theorem'}),
 Document(page_content='result; the biases logicians had expressed at the time concerning the notion of truth, biases which came vehemently to the fore when Tarski announced his results on the undefinability of truth in formal systems 1935, may have served as a deterrent to Gödel’s publication of that theorem.', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.1 The First Incompleteness Theorem'}),
 Document(page_content='We now describe the proof of the two theorems, formulating Gödel’s results in Peano arithmetic. Gödel himself used a system related to that defined in Principia Mathematica, but containing Peano arithmetic. In our presentation of the First and Second Incompleteness Theorems we refer to Peano arithmetic as P, following Gödel’s notation.', metadata={'Header 1': 'Kurt Gödel', 'Header 2': '2. Gödel’s Mathematical Work', 'Header 3': '2.2 The Incompleteness Theorems', 'Header 4': '2.2.2 The proof of the First Incompleteness Theorem'})]

限制

不同 HTML 文档之间的结构可能会有很大差异，尽管 HTMLHeaderTextSplitter 会尝试将所有“相关”的标题附加到任何给定的块上，但有时它可能会错过某些标题。例如，该算法假设了一个信息层次结构，其中标题始终位于与相关文本“上方”的节点上，即先前的兄弟节点、祖先以及它们的组合。在本文档编写时的以下新闻文章中，文档的结构是这样的，顶级标题的文本虽然被标记为 "h1"，但它位于与我们期望它“上方”的文本元素不同的独立子树中——因此我们可以观察到 "h1" 元素及其相关文本没有出现在块元数据中（但是，在适用的情况下，我们确实看到了 "h2" 及其相关文本）：

url = "https://www.cnn.com/2023/09/25/weather/el-nino-winter-us-climate/index.html"
 
headers_to_split_on = [
    ("h1", "Header 1"),
    ("h2", "Header 2"),
]
 
html_splitter = HTMLHeaderTextSplitter(headers_to_split_on=headers_to_split_on)
html_header_splits = html_splitter.split_text_from_url(url)
print(html_header_splits[1].page_content[:500])

No two El Niño winters are the same, but many have temperature and precipitation trends in common.  
Average conditions during an El Niño winter across the continental US.  
One of the major reasons is the position of the jet stream, which often shifts south during an El Niño winter. This shift typically brings wetter and cooler weather to the South while the North becomes drier and warmer, according to NOAA.  
Because the jet stream is essentially a river of air that storms flow through, the

代码分割器（CodeSplitter）HTML段落感知分割器（HTMLSectionAwareSplitter）