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115 lines
3.4 KiB
Markdown
115 lines
3.4 KiB
Markdown
# s01: The Agent Loop
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`[ s01 ] s02 > s03 > s04 > s05 > s06 | s07 > s08 > s09 > s10 > s11 > s12`
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> *"One loop & Bash is all you need"* -- one tool + one loop = an agent.
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## Problem
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A language model can reason about code, but it can't *touch* the real world -- can't read files, run tests, or check errors. Without a loop, every tool call requires you to manually copy-paste results back. You become the loop.
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## Solution
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```
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+--------+ +-------+ +---------+
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| User | ---> | LLM | ---> | Tool |
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| prompt | | | | execute |
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+--------+ +---+---+ +----+----+
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^ |
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| tool_result |
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+----------------+
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(loop until stop_reason != "tool_use")
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```
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One exit condition controls the entire flow. The loop runs until the model stops calling tools.
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## How It Works
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1. User prompt becomes the first message.
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```python
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messages.append({"role": "user", "content": query})
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```
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2. Send messages + tool definitions to the LLM.
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```python
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response = client.messages.create(
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model=MODEL, system=SYSTEM, messages=messages,
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tools=TOOLS, max_tokens=8000,
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)
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```
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3. Append the assistant response. Check `stop_reason` -- if the model didn't call a tool, we're done.
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```python
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messages.append({"role": "assistant", "content": response.content})
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if response.stop_reason != "tool_use":
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return
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```
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4. Execute each tool call, collect results, append as a user message. Loop back to step 2.
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```python
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results = []
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for block in response.content:
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if block.type == "tool_use":
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output = run_bash(block.input["command"])
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results.append({
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"type": "tool_result",
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"tool_use_id": block.id,
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"content": output,
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})
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messages.append({"role": "user", "content": results})
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```
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Assembled into one function:
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```python
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def agent_loop(query):
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messages = [{"role": "user", "content": query}]
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while True:
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response = client.messages.create(
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model=MODEL, system=SYSTEM, messages=messages,
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tools=TOOLS, max_tokens=8000,
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)
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messages.append({"role": "assistant", "content": response.content})
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if response.stop_reason != "tool_use":
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return
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results = []
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for block in response.content:
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if block.type == "tool_use":
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output = run_bash(block.input["command"])
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results.append({
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"type": "tool_result",
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"tool_use_id": block.id,
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"content": output,
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})
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messages.append({"role": "user", "content": results})
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```
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That's the entire agent in under 30 lines. Everything else in this course layers on top -- without changing the loop.
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## What Changed
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| Component | Before | After |
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|---------------|------------|--------------------------------|
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| Agent loop | (none) | `while True` + stop_reason |
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| Tools | (none) | `bash` (one tool) |
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| Messages | (none) | Accumulating list |
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| Control flow | (none) | `stop_reason != "tool_use"` |
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## Try It
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```sh
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cd learn-claude-code
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python agents/s01_agent_loop.py
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```
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1. `Create a file called hello.py that prints "Hello, World!"`
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2. `List all Python files in this directory`
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3. `What is the current git branch?`
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4. `Create a directory called test_output and write 3 files in it`
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