langchain-basic-agent

langchain-basic-agent

Demonstrates how to integrate Agent Assembly with LangChain to enforce governance policy on tool calls before execution.

What this example demonstrates

• Initializing Agent Assembly with init_assembly().
• Wrapping LangChain tools with AssemblyCallbackHandler + a governance interceptor.
• Running an allowed tool call (get_weather).
• Running a denied tool call (delete_files — blocked by a policy rule).
• Running a pending tool call (send_email — requires human approval; auto-denied in offline mode).
• How ToolExecutionBlockedError is raised when a tool is blocked.

Prerequisites

Requirement	Version
Python	>= 3.12
uv	latest
Agent Assembly Python SDK	>= 0.0.1b2

No running Agent Assembly gateway is required for the offline demo.

Setup

cd python/langchain-basic-agent
uv sync --extra dev

Run

uv run python src/main.py

Expected output

==============================================================
  Agent Assembly — LangChain Basic Agent Demo
==============================================================

Initializing Agent Assembly (gateway: http://localhost:8080, sdk-only mode)...
  Agent:    langchain-demo-agent
  Gateway:  http://localhost:8080
  Mode:     sdk-only (offline demo)

Policy rules (local simulation of gateway policy):
  DENY    — delete_files, write_file  (destructive operations)
  PENDING — send_email                (requires human approval)
  ALLOW   — everything else

Running governed tool calls:
--------------------------------------------
  → get_weather({"city": "London"})
     ✅ ALLOWED  — 🌤  Weather in {"city": "London"}: 22°C, partly cloudy (mock response)

  → delete_files({"path": "/etc/passwd"})
     ❌ BLOCKED  — Tool 'delete_files' is blocked by policy rule 'deny_destructive_operations'.

  → send_email({"to": "all@company.com", "subject": "Hello", "body": "World"})
     ❌ BLOCKED  — Tool 'send_email' requires approval, but no approver is available in offline mode.

Assembly context shut down.

Run tests

uv run pytest tests/ -v

Switching to production mode

1. Start an Agent Assembly gateway or use your SaaS workspace URL.
2. Copy .env.example to .env and fill in your credentials.
3. Run with gateway environment variables:

AGENT_ASSEMBLY_GATEWAY_URL=http://localhost:8080 \
AGENT_ASSEMBLY_API_KEY=your-key \
uv run python src/main.py

In production, remove the mode="sdk-only" argument from init_assembly() and replace LocalPolicyEngine with the gateway-backed interceptor. The SDK will enforce policy rules configured in the gateway automatically.

Troubleshooting

Problem	Fix
ModuleNotFoundError: agent_assembly	Run uv sync first
ModuleNotFoundError: langchain_core	Run uv sync — langchain-core is a required dependency
ToolExecutionBlockedError in tests	Expected — the deny/pending policy rules are intentional

Links

• Agent Assembly Python SDK
• Agent Assembly Examples
• Python Examples