langchain-upgrade-migration

# LangChain Upgrade Migration

## Overview
Guide for upgrading LangChain versions safely with migration strategies for breaking changes.

## Prerequisites
- Existing LangChain application
- Version control with current code committed
- Test suite covering core functionality
- Staging environment for validation

## Instructions

### Step 1: Check Current Versions
```bash
pip show langchain langchain-core langchain-openai langchain-community

# Output current requirements
pip freeze | grep -i langchain > langchain_current.txt
```

### Step 2: Review Breaking Changes
```python
# Key breaking changes by version:

# 0.1.x -> 0.2.x (Major restructuring)
# - langchain-core extracted as separate package
# - Imports changed from langchain.* to langchain_core.*
# - ChatModels moved to provider packages

# 0.2.x -> 0.3.x (LCEL standardization)
# - Legacy chains deprecated
# - AgentExecutor changes
# - Memory API updates

# Check migration guides:
# https://python.langchain.com/docs/versions/migrating_chains/
```

### Step 3: Update Import Paths
```python
# OLD (pre-0.2):
from langchain.chat_models import ChatOpenAI
from langchain.prompts import ChatPromptTemplate
from langchain.chains import LLMChain

# NEW (0.3+):
from langchain_openai import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.output_parsers import StrOutputParser

# Migration script
import re

def migrate_imports(content: str) -> str:
    """Migrate old imports to new pattern."""
    migrations = [
        (r"from langchain\.chat_models import ChatOpenAI",
         "from langchain_openai import ChatOpenAI"),
        (r"from langchain\.llms import OpenAI",
         "from langchain_openai import OpenAI"),
        (r"from langchain\.prompts import",
         "from langchain_core.prompts import"),
        (r"from langchain\.schema import",
         "from langchain_core.messages import"),
        (r"from langchain\.callbacks import",
         "from langchain_core.callbacks import"