core: Add ruff rules D (docstring) (#29406)

This ensures that the code is properly documented:
https://docs.astral.sh/ruff/rules/#pydocstyle-d

Related to #21983

libs/core/langchain_core/prompts/base.py

@@ -1,3 +1,5 @@
+"""Base class for prompt templates."""
+
 from __future__ import annotations
 
 import contextlib
@@ -98,6 +100,7 @@ class BasePromptTemplate(
     @classmethod
     def get_lc_namespace(cls) -> list[str]:
         """Get the namespace of the langchain object.
+
         Returns ["langchain", "schema", "prompt_template"].
         """
         return ["langchain", "schema", "prompt_template"]
@@ -105,6 +108,7 @@ class BasePromptTemplate(
     @classmethod
     def is_lc_serializable(cls) -> bool:
         """Return whether this class is serializable.
+
         Returns True.
         """
         return True
@@ -190,6 +194,7 @@ class BasePromptTemplate(
         _inner_input = self._validate_input(inner_input)
         return await self.aformat_prompt(**_inner_input)
 
+    @override
     def invoke(
         self, input: dict, config: Optional[RunnableConfig] = None, **kwargs: Any
     ) -> PromptValue:
@@ -215,6 +220,7 @@ class BasePromptTemplate(
             serialized=self._serialized,
         )
 
+    @override
     async def ainvoke(
         self, input: dict, config: Optional[RunnableConfig] = None, **kwargs: Any
     ) -> PromptValue:

libs/core/langchain_core/prompts/chat.py

@@ -22,6 +22,7 @@ from pydantic import (
     SkipValidation,
     model_validator,
 )
+from typing_extensions import override
 
 from langchain_core._api import deprecated
 from langchain_core.load import Serializable
@@ -57,13 +58,17 @@ class BaseMessagePromptTemplate(Serializable, ABC):
     @classmethod
     def is_lc_serializable(cls) -> bool:
         """Return whether or not the class is serializable.
+
         Returns: True.
         """
         return True
 
     @classmethod
     def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
+        """Get the namespace of the langchain object.
+
+        Default namespace is ["langchain", "prompts", "chat"].
+        """
         return ["langchain", "prompts", "chat"]
 
     @abstractmethod
@@ -79,7 +84,6 @@ class BaseMessagePromptTemplate(Serializable, ABC):
 
     async def aformat_messages(self, **kwargs: Any) -> list[BaseMessage]:
         """Async format messages from kwargs.
-        Should return a list of BaseMessages.
 
         Args:
             **kwargs: Keyword arguments to use for formatting.
@@ -211,14 +215,18 @@ class MessagesPlaceholder(BaseMessagePromptTemplate):
     """Maximum number of messages to include. If None, then will include all.
     Defaults to None."""
 
-    @classmethod
-    def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
-        return ["langchain", "prompts", "chat"]
-
     def __init__(
         self, variable_name: str, *, optional: bool = False, **kwargs: Any
     ) -> None:
+        """Create a messages placeholder.
+
+        Args:
+            variable_name: Name of variable to use as messages.
+            optional: If True format_messages can be called with no arguments and will
+                return an empty list. If False then a named argument with name
+                `variable_name` must be passed in, even if the value is an empty list.
+                Defaults to False.]
+        """
         # mypy can't detect the init which is defined in the parent class
         # b/c these are BaseModel classes.
         super().__init__(  # type: ignore
@@ -294,11 +302,6 @@ class BaseStringMessagePromptTemplate(BaseMessagePromptTemplate, ABC):
     additional_kwargs: dict = Field(default_factory=dict)
     """Additional keyword arguments to pass to the prompt template."""
 
-    @classmethod
-    def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
-        return ["langchain", "prompts", "chat"]
-
     @classmethod
     def from_template(
         cls: type[MessagePromptTemplateT],
@@ -424,11 +427,6 @@ class ChatMessagePromptTemplate(BaseStringMessagePromptTemplate):
     role: str
     """Role of the message."""
 
-    @classmethod
-    def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
-        return ["langchain", "prompts", "chat"]
-
     def format(self, **kwargs: Any) -> BaseMessage:
         """Format the prompt template.
 
@@ -483,11 +481,6 @@ class _StringImageMessagePromptTemplate(BaseMessagePromptTemplate):
 
     _msg_class: type[BaseMessage]
 
-    @classmethod
-    def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
-        return ["langchain", "prompts", "chat"]
-
     @classmethod
     def from_template(
         cls: type[_StringImageMessagePromptTemplateT],
@@ -719,34 +712,22 @@ class AIMessagePromptTemplate(_StringImageMessagePromptTemplate):
 
     _msg_class: type[BaseMessage] = AIMessage
 
-    @classmethod
-    def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
-        return ["langchain", "prompts", "chat"]
-
 
 class SystemMessagePromptTemplate(_StringImageMessagePromptTemplate):
     """System message prompt template.
+
     This is a message that is not sent to the user.
     """
 
     _msg_class: type[BaseMessage] = SystemMessage
 
-    @classmethod
-    def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
-        return ["langchain", "prompts", "chat"]
-
 
 class BaseChatPromptTemplate(BasePromptTemplate, ABC):
     """Base class for chat prompt templates."""
 
     @property
+    @override
     def lc_attributes(self) -> dict:
-        """Return a list of attribute names that should be included in the
-        serialized kwargs. These attributes must be accepted by the
-        constructor.
-        """
         return {"input_variables": self.input_variables}
 
     def format(self, **kwargs: Any) -> str:
@@ -968,8 +949,9 @@ class ChatPromptTemplate(BaseChatPromptTemplate):
             input_variables: A list of the names of the variables whose values are
                 required as inputs to the prompt.
             optional_variables: A list of the names of the variables for placeholder
-            or MessagePlaceholder that are optional. These variables are auto inferred
-            from the prompt and user need not provide them.
+                or MessagePlaceholder that are optional.
+                These variables are auto inferred from the prompt and user need not
+                provide them.
             partial_variables: A dictionary of the partial variables the prompt
                 template carries. Partial variables populate the template so that you
                 don't need to pass them in every time you call the prompt.

libs/core/langchain_core/prompts/image.py

@@ -1,3 +1,5 @@
+"""Image prompt template for a multimodal model."""
+
 from typing import Any
 
 from pydantic import Field
@@ -21,6 +23,7 @@ class ImagePromptTemplate(BasePromptTemplate[ImageURL]):
     Options are: 'f-string', 'mustache', 'jinja2'."""
 
     def __init__(self, **kwargs: Any) -> None:
+        """Create an image prompt template."""
         if "input_variables" not in kwargs:
             kwargs["input_variables"] = []
 

libs/core/langchain_core/prompts/pipeline.py

@@ -1,3 +1,5 @@
+"""[DEPRECATED] Pipeline prompt template."""
+
 from typing import Any
 from typing import Optional as Optional
 
@@ -23,7 +25,9 @@ def _get_inputs(inputs: dict, input_variables: list[str]) -> dict:
     ),
 )
 class PipelinePromptTemplate(BasePromptTemplate):
-    """This has been deprecated in favor of chaining individual prompts together in your
+    """[DEPRECATED] Pipeline prompt template.
+
+    This has been deprecated in favor of chaining individual prompts together in your
     code. E.g. using a for loop, you could do:
 
     .. code-block:: python

libs/core/langchain_core/prompts/prompt.py

@@ -7,6 +7,7 @@ from pathlib import Path
 from typing import TYPE_CHECKING, Any, Optional, Union
 
 from pydantic import BaseModel, model_validator
+from typing_extensions import override
 
 from langchain_core.prompts.string import (
     DEFAULT_FORMATTER_MAPPING,
@@ -58,14 +59,15 @@ class PromptTemplate(StringPromptTemplate):
     """
 
     @property
+    @override
     def lc_attributes(self) -> dict[str, Any]:
         return {
             "template_format": self.template_format,
         }
 
     @classmethod
+    @override
     def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
         return ["langchain", "prompts", "prompt"]
 
     template: str
@@ -116,6 +118,7 @@ class PromptTemplate(StringPromptTemplate):
 
         return values
 
+    @override
     def get_input_schema(self, config: RunnableConfig | None = None) -> type[BaseModel]:
         """Get the input schema for the prompt.
 

libs/core/langchain_core/prompts/string.py

@@ -65,6 +65,7 @@ def jinja2_formatter(template: str, /, **kwargs: Any) -> str:
 
 def validate_jinja2(template: str, input_variables: list[str]) -> None:
     """Validate that the input variables are valid for the template.
+
     Issues a warning if missing or extra variables are found.
 
     Args:

libs/core/langchain_core/prompts/structured.py

@@ -1,3 +1,5 @@
+"""Structured prompt template for a language model."""
+
 from collections.abc import Iterator, Mapping, Sequence
 from typing import (
     Any,
@@ -7,6 +9,7 @@ from typing import (
 )
 
 from pydantic import BaseModel, Field
+from typing_extensions import override
 
 from langchain_core._api.beta_decorator import beta
 from langchain_core.language_models.base import BaseLanguageModel
@@ -41,6 +44,14 @@ class StructuredPrompt(ChatPromptTemplate):
         template_format: PromptTemplateFormat = "f-string",
         **kwargs: Any,
     ) -> None:
+        """Create a structured prompt template.
+
+        Args:
+            messages: sequence of messages.
+            schema_: schema for the structured prompt.
+            structured_output_kwargs: additional kwargs for structured output.
+            template_format: template format for the prompt.
+        """
         schema_ = schema_ or kwargs.pop("schema")
         structured_output_kwargs = structured_output_kwargs or {}
         for k in set(kwargs).difference(get_pydantic_field_names(self.__class__)):
@@ -107,6 +118,7 @@ class StructuredPrompt(ChatPromptTemplate):
         """
         return cls(messages, schema, **kwargs)
 
+    @override
     def __or__(
         self,
         other: Union[