84 lines
2.9 KiB
Markdown
84 lines
2.9 KiB
Markdown
---
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layout: default
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title: "Node"
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parent: Core Abstraction
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nav_order: 1
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---
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# Node
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A **Node** is the smallest building block of Mini LLM Flow. Each Node has three lifecycle methods:
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1. **`prep(shared)`**
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- Optionally preprocess data before calling your LLM or doing heavy computation.
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- Often used for tasks like reading files, chunking text, or validation.
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- Returns `prep_res`, which will be passed to both `exec()` and `post()`.
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2. **`exec(shared, prep_res)`**
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- The main execution step, typically where you call your LLM or any external APIs.
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- Returns `exec_res`, which is passed to `post()`.
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3. **`post(shared, prep_res, exec_res)`**
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- Optionally perform post-processing, such as writing results back to the `shared` store or deciding the next action.
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- Often used to finalize outputs, trigger next steps, or log results.
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- Returns a **string** to specify the next action (`"default"` if nothing or `None` is returned).
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## Fault Tolerance & Retries
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Nodes in Mini LLM Flow can **retry** execution if `exec()` raises an exception. You control this via a `max_retries` parameter when you create the Node. By default, `max_retries = 1` (meaning no retry).
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```python
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my_node = SummarizeFile(max_retries=3)
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```
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When an exception occurs in `exec()`, the Node automatically retries until:
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- It either succeeds, **or**
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- The Node has retried `max_retries - 1` times already and fails on the last attempt.
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If you want to **gracefully handle** the error rather than raising it, you can override:
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```python
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def process_after_fail(self, shared, prep_res, exc):
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raise exc
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```
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By **default**, it just re-raises `exc`. But you can return a fallback result instead. That fallback result becomes the `exec_res` passed to `post()`.
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## Minimal Example
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```python
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class SummarizeFile(Node):
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def prep(self, shared):
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filename = self.params["filename"]
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return shared["data"][filename]
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def exec(self, shared, prep_res):
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if not prep_res:
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raise ValueError("Empty file content!")
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prompt = f"Summarize this text in 10 words: {prep_res}"
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summary = call_llm(prompt) # might fail
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return summary
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def process_after_fail(self, shared, prep_res, exc):
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# Provide a simple fallback instead of crashing
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return "There was an error processing your request."
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def post(self, shared, prep_res, exec_res):
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filename = self.params["filename"]
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shared["summary"][filename] = exec_res
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# Return "default" by not returning anything
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summarize_node = SummarizeFile(max_retries=3)
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# Run the node standalone for testing (calls prep->exec->post).
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# If exec() fails, it retries up to 3 times before calling process_after_fail().
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summarize_node.set_params({"filename": "test_file.txt"})
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action_result = summarize_node.run(shared)
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print("Action returned:", action_result) # Usually "default"
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print("Summary stored:", shared["summary"].get("test_file.txt"))
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```
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