core: Add support to accept PDF in ChatPromptTemplate.

>
>
Co-authored-by: czhu24 <[email protected]>

libs/core/extended_testing_deps.txt

@@ -1 +1,2 @@
 jinja2>=3,<4
+pypdf>=5,<6

libs/core/langchain_core/prompts/chat.py

@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+import base64
+import io
 from abc import ABC, abstractmethod
 from collections.abc import Sequence
 from pathlib import Path
@@ -22,6 +24,7 @@
     SkipValidation,
     model_validator,
 )
+from pypdf import PdfReader
 
 from langchain_core._api import deprecated
 from langchain_core.load import Serializable
@@ -48,6 +51,22 @@
 from langchain_core.utils.interactive_env import is_interactive_env
 
 
+# extract pdf into bytes
+def extract_pdf_text(pdf_data: bytes) -> str:
+    # Decode the base64 back into bytes
+    pdf_bytes = base64.b64decode(pdf_data)
+    pdf_text = ""
+
+    # Read the PDF and extract text
+    with io.BytesIO(pdf_bytes) as pdf_file:
+        reader = PdfReader(pdf_file)
+        for page in reader.pages:
+            extracted_text = page.extract_text()
+            pdf_text += extracted_text + "\n"
+
+    return pdf_text
+
+
 class BaseMessagePromptTemplate(Serializable, ABC):
     """Base class for message prompt templates."""
 
@@ -468,6 +487,10 @@ class _ImageTemplateParam(TypedDict, total=False):
     image_url: Union[str, dict]
 
 
+class _PdfTemplateParam(TypedDict, total=False):
+    pdf: Union[str, dict]
+
+
 class _StringImageMessagePromptTemplate(BaseMessagePromptTemplate):
     """Human message prompt template. This is a message sent from the user."""
 
@@ -571,6 +594,12 @@ def from_template(
                         msg = f"Invalid image template: {tmpl}"
                         raise ValueError(msg)
                     prompt.append(img_template_obj)
+                elif isinstance(tmpl, dict) and "data" in tmpl:
+                    if tmpl.get("mime_type") == "application/pdf":
+                        pdf_template = cast(_PdfTemplateParam, tmpl)["data"]
+                        pdf_text = extract_pdf_text(pdf_template)
+
+                        prompt.append(PromptTemplate.from_template(pdf_text))
                 else:
                     msg = f"Invalid template: {tmpl}"
                     raise ValueError(msg)

libs/core/tests/unit_tests/prompts/test_chat.py

@@ -36,6 +36,36 @@
 from tests.unit_tests.pydantic_utils import _normalize_schema
 
 
+def test_create_pdf_chat_prompt() -> None:
+    """Test chat prompt with pdf data as bytes."""
+    file_path = (
+        Path(__file__).parent.parent.parent.parent.parent
+        / "community/tests/examples/hello.pdf"
+    )
+
+    with open(file_path, "rb") as file:
+        file_data = file.read()
+
+    pdf_data = base64.b64encode(file_data).decode("utf-8")
+    prompt = ChatPromptTemplate(
+        [
+            (
+                "human",
+                [
+                    {"type": "media", "mime_type": "application/pdf", "data": pdf_data},
+                ],
+            )
+        ]
+    )
+
+    expected_prompt = PromptTemplate(template="Hello world!\n1\n")
+
+    assert len(prompt.messages) == 1
+    output_prompt = prompt.messages[0]
+    assert isinstance(output_prompt, HumanMessagePromptTemplate)
+    assert output_prompt.prompt == [expected_prompt]
+
+
 @pytest.fixture
 def messages() -> list[BaseMessagePromptTemplate]:
     """Create messages."""