LangChain v0.2

LangChain v0.2 was released in May 2024. This release includes a number of breaking changes and deprecations. This document contains a guide on upgrading to 0.2.x, as well as a list of deprecations and breaking changes.

Migration

This documentation will help you upgrade your code to LangChain 0.2.x.. To prepare for migration, we first recommend you take the following steps:

1. install the 0.2.x versions of langchain-core, langchain and upgrade to recent versions of other packages that you may be using (e.g. langgraph, langchain-community, langchain-openai, etc.)
2. Verify that your code runs properly with the new packages (e.g., unit tests pass)
3. Install a recent version of langchain-cli , and use the tool to replace old imports used by your code with the new imports. (See instructions below.)
4. Manually resolve any remaining deprecation warnings
5. Re-run unit tests

Upgrade to new imports

We created a tool to help migrate your code. This tool is still in beta and may not cover all cases, but we hope that it will help you migrate your code more quickly.

The migration script has the following limitations:

1. It’s limited to helping users move from old imports to new imports. It doesn’t help address other deprecations.
2. It can’t handle imports that involve as .
3. New imports are always placed in global scope, even if the old import that was replaced was located inside some local scope (e..g, function body).
4. It will likely miss some deprecated imports.

Here is an example of the import changes that the migration script can help apply automatically:

From Package	To Package	Deprecated Import	New Import
langchain	langchain-community	from langchain.vectorstores import InMemoryVectorStore	from langchain_community.vectorstores import InMemoryVectorStore
langchain-community	langchain_openai	from langchain_community.chat_models import ChatOpenAI	from langchain_openai import ChatOpenAI
langchain-community	langchain-core	from langchain_community.document_loaders import Blob	from langchain_core.document_loaders import Blob
langchain	langchain-core	from langchain.schema.document import Document	from langchain_core.documents import Document
langchain	langchain-text-splitters	from langchain.text_splitter import RecursiveCharacterTextSplitter	from langchain_text_splitters import RecursiveCharacterTextSplitter

Deprecation timeline

We have two main types of deprecations:

1. Code that was moved from langchain into another package (e.g, langchain-community)

If you try to import it from langchain, the import will keep on working, but will raise a deprecation warning. The warning will provide a replacement import statement.

python -c "from langchain.document_loaders.markdown import UnstructuredMarkdownLoader"

   ```

```python
LangChainDeprecationWarning: Importing UnstructuredMarkdownLoader from langchain.document_loaders is deprecated. Please replace deprecated imports:

>> from langchain.document_loaders import UnstructuredMarkdownLoader

with new imports of:

>> from langchain_community.document_loaders import UnstructuredMarkdownLoader
   ```

We will continue supporting the imports in `langchain` until release 0.4 as long as the relevant package where the code lives is installed. (e.g., as long as `langchain_community` is installed.)

However, we advise for users to not rely on these imports and instead migrate to the new imports. To help with this process, we’re releasing a migration script via the LangChain CLI. See further instructions in migration guide.

2. Code that has better alternatives available and will eventually be removed, so there’s only a single way to do things. (e.g., `predict_messages` method in ChatModels has been deprecated in favor of `invoke`).

Many of these were marked for removal in 0.2. We have bumped the removal to 0.3.


#### Installation

```bash
pip install langchain-cli
langchain-cli --version # <-- Make sure the version is at least 0.0.22

Usage

Given that the migration script is not perfect, you should make sure you have a backup of your code first (e.g., using version control like git).

You will need to run the migration script twice as it only applies one import replacement per run.

For example, say your code still uses from langchain.chat_models import ChatOpenAI:

After the first run, you’ll get: from langchain_community.chat_models import ChatOpenAI After the second run, you’ll get: from langchain_openai import ChatOpenAI

# Run a first time
# Will replace from langchain.chat_models import ChatOpenAI
langchain-cli migrate [path to code] --diff # Preview
langchain-cli migrate [path to code] # Apply

# Run a second time to apply more import replacements
langchain-cli migrate [path to code] --diff # Preview
langchain-cli migrate [path to code] # Apply

Other options

# See help menu
langchain-cli migrate --help
# Preview Changes without applying
langchain-cli migrate --diff [path to code]
# Run on code including ipython notebooks
# Apply all import updates except for updates from langchain to langchain-core
langchain-cli migrate --disable langchain_to_core --include-ipynb [path to code]

Deprecations and breaking changes

This code contains a list of deprecations and removals in the langchain and langchain-core packages.

Breaking changes in 0.2.0

As of release 0.2.0, langchain is required to be integration-agnostic. This means that code in langchain should not by default instantiate any specific chat models, llms, embedding models, vectorstores etc; instead, the user will be required to specify those explicitly.

The following functions and classes require an explicit LLM to be passed as an argument:

• langchain.agents.agent_toolkits.vectorstore.toolkit.VectorStoreToolkit
• langchain.agents.agent_toolkits.vectorstore.toolkit.VectorStoreRouterToolkit
• langchain.chains.openai_functions.get_openapi_chain
• langchain.chains.router.MultiRetrievalQAChain.from_retrievers
• langchain.indexes.VectorStoreIndexWrapper.query
• langchain.indexes.VectorStoreIndexWrapper.query_with_sources
• langchain.indexes.VectorStoreIndexWrapper.aquery_with_sources
• langchain.chains.flare.FlareChain

The following classes now require passing an explicit Embedding model as an argument:

• langchain.indexes.VectostoreIndexCreator

The following code has been removed:

• langchain.natbot.NatBotChain.from_default removed in favor of the from_llm class method.

Deprecations

We have two main types of deprecations:

1. Code that was moved from langchain into another package (e.g, langchain-community)

   If you try to import it from langchain, the import will keep on working, but will raise a deprecation warning. The warning will provide a replacement import statement.

   python -c "from langchain.document_loaders.markdown import UnstructuredMarkdownLoader"

   LangChainDeprecationWarning: Importing UnstructuredMarkdownLoader from langchain.document_loaders is deprecated. Please replace deprecated imports:
   
   >> from langchain.document_loaders import UnstructuredMarkdownLoader
   
   with new imports of:
   
   >> from langchain_community.document_loaders import UnstructuredMarkdownLoader

   We will continue supporting the imports in langchain until release 0.4 as long as the relevant package where the code lives is installed. (e.g., as long as langchain_community is installed.)

   However, we advise for users to not rely on these imports and instead migrate to the new imports. To help with this process, we’re releasing a migration script via the LangChain CLI. See further instructions in migration guide.

2. Code that has better alternatives available and will eventually be removed, so there’s only a single way to do things. (e.g., predict_messages method in ChatModels has been deprecated in favor of invoke).

   Many of these were marked for removal in 0.2. We have bumped the removal to 0.3.