docs: added community modules descriptions (#17827)

API Reference: Several `community` modules (like
[adapter](https://api.python.langchain.com/en/latest/community_api_reference.html#module-langchain_community.adapters)
module) are missing descriptions. It happens when langchain was split to
the core, langchain and community packages.
- Copied module descriptions from other packages
- Fixed several descriptions to the consistent format.

libs/community/langchain_community/adapters/__init__.py

@@ -0,0 +1,8 @@
+"""**Adapters** are used to adapt LangChain models to other APIs.
+
+LangChain integrates with many model providers.
+While LangChain has its own message and model APIs,
+LangChain has also made it as easy as
+possible to explore other models by exposing an **adapter** to adapt LangChain
+models to the other APIs, as to the OpenAI API.
+"""

libs/community/langchain_community/agent_toolkits/__init__.py

@@ -1,17 +1,5 @@
-"""Agent toolkits contain integrations with various resources and services.
-
-LangChain has a large ecosystem of integrations with various external resources
-like local and remote file systems, APIs and databases.
-
-These integrations allow developers to create versatile applications that combine the
-power of LLMs with the ability to access, interact with and manipulate external
-resources.
-
-When developing an application, developers should inspect the capabilities and
-permissions of the tools that underlie the given agent toolkit, and determine
-whether permissions of the given toolkit are appropriate for the application.
-
-See [Security](https://python.langchain.com/docs/security) for more information.
+"""**Toolkits** are sets of tools that can be used to interact with
+various services and APIs.
 """
 from langchain_community.agent_toolkits.ainetwork.toolkit import AINetworkToolkit
 from langchain_community.agent_toolkits.amadeus.toolkit import AmadeusToolkit

libs/community/langchain_community/chat_message_histories/__init__.py

@@ -1,3 +1,20 @@
+"""**Chat message history** stores a history of the message interactions in a chat.
+
+
+**Class hierarchy:**
+
+.. code-block::
+
+    BaseChatMessageHistory --> <name>ChatMessageHistory  # Examples: FileChatMessageHistory, PostgresChatMessageHistory
+
+**Main helpers:**
+
+.. code-block::
+
+    AIMessage, HumanMessage, BaseMessage
+
+"""  # noqa: E501
+
 from langchain_community.chat_message_histories.astradb import (
     AstraDBChatMessageHistory,
 )

libs/community/langchain_community/example_selectors/__init__.py

@@ -1,4 +1,11 @@
-"""Logic for selecting examples to include in prompts."""
+"""**Example selector** implements logic for selecting examples to include them
+in prompts.
+This allows us to select examples that are most relevant to the input.
+
+There could be multiple strategies for selecting examples. For example, one could
+select examples based on the similarity of the input to the examples. Another
+strategy could be to select examples based on the diversity of the examples.
+"""
 from langchain_community.example_selectors.ngram_overlap import (
     NGramOverlapExampleSelector,
     ngram_overlap_score,

libs/community/langchain_community/indexes/__init__.py

@@ -0,0 +1,13 @@
+"""**Index** is used to avoid writing duplicated content
+into the vectostore and to avoid over-writing content if it's unchanged.
+
+Indexes also :
+
+* Create knowledge graphs from data.
+
+* Support indexing workflows from LangChain data loaders to vectorstores.
+
+Importantly, Index keeps on working even if the content being written is derived
+via a set of transformations from some source content (e.g., indexing children
+documents that were derived from parent documents by chunking.)
+"""

libs/community/langchain_community/storage/__init__.py

@@ -1,10 +1,18 @@
-"""Implementations of key-value stores and storage helpers.
+"""**Storage** is an implementation of key-value store.
 
-Module provides implementations of various key-value stores that conform
+Storage module provides implementations of various key-value stores that conform
 to a simple key-value interface.
 
-The primary goal of these storages is to support implementation of caching.
-"""
+The primary goal of these storages is to support caching.
+
+
+**Class hierarchy:**
+
+.. code-block::
+
+    BaseStore --> <name>Store  # Examples: MongoDBStore, RedisStore
+
+"""  # noqa: E501
 
 from langchain_community.storage.astradb import (
     AstraDBByteStore,

libs/langchain/langchain/indexes/__init__.py

@@ -1,15 +1,13 @@
-"""Code to support various indexing workflows.
+"""**Index** is used to avoid writing duplicated content
+into the vectostore and to avoid over-writing content if it's unchanged.
 
-Provides code to:
+Indexes also :
 
 * Create knowledge graphs from data.
 
 * Support indexing workflows from LangChain data loaders to vectorstores.
 
-For indexing workflows, this code is used to avoid writing duplicated content
-into the vectostore and to avoid over-writing content if it's unchanged.
-
-Importantly, this keeps on working even if the content being written is derived
+Importantly, Index keeps on working even if the content being written is derived
 via a set of transformations from some source content (e.g., indexing children
 documents that were derived from parent documents by chunking.)
 """