LangChain - 老张API

LangChain is a powerful framework for building large language model (LLM) applications. Through Laozhang API, you can use various mainstream AI models in LangChain, building complex AI application chains.

Quick Integration

1. Install Dependencies

pip install langchain langchain-openai

npm install langchain @langchain/openai

2. Configuration

import os
from langchain_openai import ChatOpenAI

# Set environment variables
os.environ["OPENAI_API_BASE"] = "https://api2.laozhang.ai/v1"
os.environ["OPENAI_API_KEY"] = "Your Laozhang API key"

# Initialize model
llm = ChatOpenAI(
    model="gpt-4-turbo",
    temperature=0.7,
    max_tokens=2000
)

# Test call
response = llm.invoke("Hello!")
print(response.content)

import { ChatOpenAI } from "@langchain/openai";

// Initialize model
const llm = new ChatOpenAI({
  modelName: "gpt-4-turbo",
  temperature: 0.7,
  maxTokens: 2000,
  configuration: {
    baseURL: "https://api2.laozhang.ai/v1",
    apiKey: "Your Laozhang API key",
  },
});

// Test call
const response = await llm.invoke("Hello!");
console.log(response.content);

import { ChatOpenAI } from "@langchain/openai";

// Initialize model
const llm = new ChatOpenAI({
  modelName: "gpt-4-turbo",
  temperature: 0.7,
  maxTokens: 2000,
  configuration: {
    baseURL: "https://api2.laozhang.ai/v1",
    apiKey: process.env.OPENAI_API_KEY || "",
  },
});

// Test call
const response = await llm.invoke("Hello!");
console.log(response.content);

API Key ManagementIt’s recommended to use environment variables to manage API Keys, avoiding hardcoding keys in code.Visit Laozhang API Console to obtain your API Key.

Supported Models

LangChain supports the following models through Laozhang API:

Text Generation Models

Model Series	Model ID	Context Length	Features
GPT-4 Turbo	`gpt-4-turbo`	128K	Strong reasoning ability
GPT-3.5 Turbo	`gpt-3.5-turbo`	16K	Fast and economical
Claude Sonnet	`claude-sonnet-4`	200K	Long context support
Gemini Pro	`gemini-2.5-pro`	1M	Multimodal support

Embedding Models

Model	Dimension	Features
`text-embedding-ada-002`	1536	High-quality semantic understanding
`text-embedding-3-small`	512	Lightweight, fast
`text-embedding-3-large`	3072	Highest precision

Core Concepts

1. Chains

Chains are the core concept of LangChain, connecting multiple components:

from langchain.chains import LLMChain
from langchain.prompts import PromptTemplate

# Create prompt template
prompt = PromptTemplate(
    input_variables=["product"],
    template="Please write an advertising slogan for {product}:"
)

# Create chain
chain = LLMChain(llm=llm, prompt=prompt)

# Execute chain
result = chain.run(product="AI programming assistant")
print(result)

2. Prompts

Prompt template management:

from langchain.prompts import ChatPromptTemplate

# Multi-turn conversation template
prompt = ChatPromptTemplate.from_messages([
    ("system", "You are a professional {role}"),
    ("human", "{input}"),
])

# Format prompt
messages = prompt.format_messages(
    role="Python programmer",
    input="How to optimize code performance?"
)

# Call model
response = llm.invoke(messages)
print(response.content)

3. Memory

Conversation history management:

from langchain.memory import ConversationBufferMemory
from langchain.chains import ConversationChain

# Create memory
memory = ConversationBufferMemory()

# Create conversation chain
conversation = ConversationChain(
    llm=llm,
    memory=memory,
    verbose=True
)

# Multi-turn conversation
response1 = conversation.predict(input="The active project code is Atlas")
response2 = conversation.predict(input="What is the active project code?")
print(response2)  # Will remember the active project code

4. Agents

Autonomous decision-making AI agents:

from langchain.agents import initialize_agent, AgentType, Tool

# Define tools
tools = [
    Tool(
        name="Calculator",
        func=lambda x: eval(x),
        description="Useful for mathematical calculations"
    )
]

# Create agent
agent = initialize_agent(
    tools=tools,
    llm=llm,
    agent=AgentType.ZERO_SHOT_REACT_DESCRIPTION,
    verbose=True
)

# Execute task
result = agent.run("What is (25 + 75) * 2?")
print(result)

Application Scenarios

1. Document Q&A System

Build an intelligent document Q&A system:

from langchain.document_loaders import TextLoader
from langchain.text_splitter import CharacterTextSplitter
from langchain.embeddings import OpenAIEmbeddings
from langchain.vectorstores import FAISS
from langchain.chains import RetrievalQA

# Load documents
loader = TextLoader("document.txt", encoding="utf-8")
documents = loader.load()

# Split text
text_splitter = CharacterTextSplitter(
    chunk_size=1000,
    chunk_overlap=200
)
texts = text_splitter.split_documents(documents)

# Create vector database
embeddings = OpenAIEmbeddings(
    openai_api_base="https://api2.laozhang.ai/v1",
    openai_api_key="Your Laozhang API key"
)
vectorstore = FAISS.from_documents(texts, embeddings)

# Create Q&A chain
qa = RetrievalQA.from_chain_type(
    llm=llm,
    chain_type="stuff",
    retriever=vectorstore.as_retriever()
)

# Ask questions
result = qa.run("What is the main content of this document?")
print(result)

2. Multi-step Workflow

Build complex multi-step workflows:

from langchain.chains import SimpleSequentialChain

# Step 1: Generate outline
outline_chain = LLMChain(
    llm=llm,
    prompt=PromptTemplate(
        input_variables=["topic"],
        template="Please create a detailed outline for the following topic:\n\n{topic}"
    )
)

# Step 2: Expand content
content_chain = LLMChain(
    llm=llm,
    prompt=PromptTemplate(
        input_variables=["outline"],
        template="Please expand the following outline into complete content:\n\n{outline}"
    )
)

# Combine chains
workflow = SimpleSequentialChain(
    chains=[outline_chain, content_chain],
    verbose=True
)

# Execute workflow
result = workflow.run("AI Application Development Guide")
print(result)

3. Multi-model Collaboration

Use different models for different tasks:

# Use GPT-3.5 for simple tasks
light_llm = ChatOpenAI(
    model="gpt-3.5-turbo",
    temperature=0.5
)

# Use GPT-4 for complex tasks (higher quality)
expensive_llm = ChatOpenAI(
    model="gpt-4-turbo",
    temperature=0.7
)

# Simple classification task
classification = light_llm.invoke("Classify this text sentiment: This product is great!")

# Complex analysis task
analysis = expensive_llm.invoke("Please analyze this product review in depth: This product is great!")

4. Streaming Output

Support streaming output for better user experience:

from langchain.callbacks.streaming_stdout import StreamingStdOutCallbackHandler

# Create model with streaming support
streaming_llm = ChatOpenAI(
    model="gpt-4-turbo",
    temperature=0.7,
    streaming=True,
    callbacks=[StreamingStdOutCallbackHandler()]
)

# Streaming response
response = streaming_llm.invoke("Please write a short story")

Advanced Features

Custom Tools

Create custom tools:

from langchain.tools import Tool

def search_database(query: str) -> str:
    """Search database"""
    # Your database search logic
    return f"Search result for: {query}"

# Create tool
search_tool = Tool(
    name="DatabaseSearch",
    func=search_database,
    description="Search information from database. Input should be search keywords."
)

Error Handling

Implement robust error handling:

from langchain.chains import LLMChain
from langchain.callbacks import get_openai_callback

try:
    with get_openai_callback() as cb:
        result = chain.run(input="Your input")
        print(f"Total tokens: {cb.total_tokens}")
        print(f"Total cost: ${cb.total_cost}")
except Exception as e:
    print(f"Error occurred: {str(e)}")

Caching

Enable result caching to improve performance:

from langchain.cache import InMemoryCache
import langchain

# Enable cache
langchain.llm_cache = InMemoryCache()

# First call (slower)
result1 = llm.invoke("What is AI?")

# Second call (use cache, faster)
result2 = llm.invoke("What is AI?")

Best Practices

1. Prompt Optimization

Write effective prompts:

# ❌ Bad example
prompt = "Write something"

# ✅ Good example
prompt = """
You are a professional technical writer.

Task: Write an article about AI applications
Requirements:
- Word count: 1000 words
- Audience: Technical professionals
- Style: Professional yet approachable
- Structure: Introduction - Body - Conclusion
- Include: 3 practical cases

Please start writing:
"""

2. Token Management

Control token usage:

# Set max_tokens
llm = ChatOpenAI(
    model="gpt-4-turbo",
    max_tokens=1000,  # Limit output length
    temperature=0.7
)

# Monitor token usage
with get_openai_callback() as cb:
    result = chain.run(input="Your input")
    print(f"Input tokens: {cb.prompt_tokens}")
    print(f"Output tokens: {cb.completion_tokens}")
    print(f"Total tokens: {cb.total_tokens}")

3. Error Retry

Implement retry mechanism:

from tenacity import retry, stop_after_attempt, wait_exponential

@retry(
    stop=stop_after_attempt(3),
    wait=wait_exponential(multiplier=1, min=4, max=10)
)
def call_llm_with_retry(input_text):
    return llm.invoke(input_text)

# Use retry function
result = call_llm_with_retry("Your input")

4. Security Practices

Protect sensitive information:

import os
from dotenv import load_dotenv

# Load environment variables
load_dotenv()

# Use environment variables
api_key = os.getenv("OPENAI_API_KEY")
api_base = os.getenv("OPENAI_API_BASE")

# Do not hardcode API keys in code
llm = ChatOpenAI(
    openai_api_base=api_base,
    openai_api_key=api_key
)

Performance Optimization

Batch Processing

Batch process requests to improve efficiency:

from langchain.chains import LLMChain

# Create chain
chain = LLMChain(llm=llm, prompt=prompt)

# Batch processing
inputs = [
    {"product": "AI assistant"},
    {"product": "Smart home"},
    {"product": "Electric vehicle"}
]

results = chain.apply(inputs)
for result in results:
    print(result)

Asynchronous Calls

Use asynchronous calls to improve concurrency:

import asyncio
from langchain.callbacks import AsyncIteratorCallbackHandler

async def async_call():
    result = await llm.ainvoke("Hello!")
    return result

# Execute asynchronously
result = asyncio.run(async_call())

Troubleshooting

Connection Issues

Problem: Unable to connect to API Solutions:

Check if API Base URL is correct: https://api2.laozhang.ai/v1
Verify API Key validity
Check network connection
Confirm firewall settings

Rate Limiting

Problem: Request frequency too high Solutions:

Implement request rate limiting
Use batch processing
Add retry mechanism
Consider upgrading plan

Memory Issues

Problem: Conversation history is too long Solutions:

Use ConversationBufferWindowMemory to limit history
Use ConversationSummaryMemory to compress history
Regularly clean up old conversations
Use external storage

Further Learning

Official Resources

Learning Resources

Community Support

Need more help? Please visit Laozhang API Official Website or contact our support team.

​Quick Integration

​1. Install Dependencies

​2. Configuration

​Supported Models

​Text Generation Models

​Embedding Models

​Core Concepts

​1. Chains

​2. Prompts

​3. Memory

​4. Agents

​Application Scenarios

​1. Document Q&A System

​2. Multi-step Workflow

​3. Multi-model Collaboration

​4. Streaming Output

​Advanced Features

​Custom Tools

​Error Handling

​Caching

​Best Practices

​1. Prompt Optimization

​2. Token Management

​3. Error Retry

​4. Security Practices

​Performance Optimization

​Batch Processing

​Asynchronous Calls

​Troubleshooting

​Connection Issues

​Rate Limiting

​Memory Issues

​Further Learning

​Official Resources

​Learning Resources

​Community Support

Quick Integration

1. Install Dependencies

2. Configuration

Supported Models

Text Generation Models

Embedding Models

Core Concepts

1. Chains

2. Prompts

3. Memory

4. Agents

Application Scenarios

1. Document Q&A System

2. Multi-step Workflow

3. Multi-model Collaboration

4. Streaming Output

Advanced Features

Custom Tools

Error Handling

Caching

Best Practices

1. Prompt Optimization

2. Token Management

3. Error Retry

4. Security Practices

Performance Optimization

Batch Processing

Asynchronous Calls

Troubleshooting

Connection Issues

Rate Limiting

Memory Issues

Further Learning

Official Resources

Learning Resources

Community Support