community: Add warning when page_content is empty (#25955)

Page content sometimes is empty when PyMuPDF can not find text on pages.
For example, this can happen when the text of the PDF is not copyable
"by hand". Then an OCR solution is need - which is not integrated here.

This warning should accurately warn the user that some pages are lost
during this process.

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---------

Co-authored-by: Erick Friis <[email protected]>

libs/community/langchain_community/document_loaders/parsers/pdf.py

@@ -267,6 +267,7 @@ def __init__(
 
     def lazy_parse(self, blob: Blob) -> Iterator[Document]:  # type: ignore[valid-type]
         """Lazily parse the blob."""
+
         import fitz
 
         with blob.as_bytes_io() as file_path:  # type: ignore[attr-defined]
@@ -277,25 +278,49 @@ def lazy_parse(self, blob: Blob) -> Iterator[Document]:  # type: ignore[valid-ty
 
             yield from [
                 Document(
-                    page_content=page.get_text(**self.text_kwargs)
-                    + self._extract_images_from_page(doc, page),
-                    metadata=dict(
-                        {
-                            "source": blob.source,  # type: ignore[attr-defined]
-                            "file_path": blob.source,  # type: ignore[attr-defined]
-                            "page": page.number,
-                            "total_pages": len(doc),
-                        },
-                        **{
-                            k: doc.metadata[k]
-                            for k in doc.metadata
-                            if type(doc.metadata[k]) in [str, int]
-                        },
-                    ),
+                    page_content=self._get_page_content(doc, page, blob),
+                    metadata=self._extract_metadata(doc, page, blob),
                 )
                 for page in doc
             ]
 
+    def _get_page_content(
+        self, doc: fitz.fitz.Document, page: fitz.fitz.Page, blob: Blob
+    ) -> str:
+        """
+        Get the text of the page using PyMuPDF and RapidOCR and issue a warning
+        if it is empty.
+        """
+        content = page.get_text(**self.text_kwargs) + self._extract_images_from_page(
+            doc, page
+        )
+
+        if not content:
+            warnings.warn(
+                f"Warning: Empty content on page "
+                f"{page.number} of document {blob.source}"
+            )
+
+        return content
+
+    def _extract_metadata(
+        self, doc: fitz.fitz.Document, page: fitz.fitz.Page, blob: Blob
+    ) -> dict:
+        """Extract metadata from the document and page."""
+        return dict(
+            {
+                "source": blob.source,  # type: ignore[attr-defined]
+                "file_path": blob.source,  # type: ignore[attr-defined]
+                "page": page.number,
+                "total_pages": len(doc),
+            },
+            **{
+                k: doc.metadata[k]
+                for k in doc.metadata
+                if isinstance(doc.metadata[k], (str, int))
+            },
+        )
+
     def _extract_images_from_page(
         self, doc: fitz.fitz.Document, page: fitz.fitz.Page
     ) -> str: