core: use friendlier names for duplicated nodes in mermaid output

[antwhite]

Thank you for contributing to LangChain!

• PR title: "core: use friendlier names for duplicated nodes in mermaid output"

• Description: When generating the Mermaid visualization of a chain, if the chain had multiple nodes of the same type, the reid function would replace their names with the UUID node_id. This made the generated graph difficult to understand. This change deduplicates the nodes in a chain by appending an index to their names.

• Issue: None

• Discussion: Improve draw_mermaid Graph Readability for Multiple Nodes of the Same Type #27714

• Dependencies: None

• Add tests and docs:

  • Currently this functionality is not covered by unit tests, happy to add tests if you'd like

• Lint and test: Run make format, make lint and make test from the root of the package(s) you've modified. See contribution guidelines for more: https://python.langchain.com/docs/contributing/

Additional guidelines:

• Make sure optional dependencies are imported within a function.
• Please do not add dependencies to pyproject.toml files (even optional ones) unless they are required for unit tests.
• Most PRs should not touch more than one package.
• Changes should be backwards compatible.
• If you are adding something to community, do not re-import it in langchain.

If no one reviews your PR within a few days, please @-mention one of baskaryan, efriis, eyurtsev, ccurme, vbarda, hwchase17.

Example Code:

from langchain_core.runnables import RunnablePassthrough

def fake_llm(prompt: str) -> str: # Fake LLM for the example
    return "completion"

runnable = {
    'llm1':  fake_llm,
    'llm2':  fake_llm,
} | RunnablePassthrough.assign(
    total_chars=lambda inputs: len(inputs['llm1'] + inputs['llm2'])
)

print(runnable.get_graph().draw_mermaid(with_styles=False))

Before

graph TD;
	Parallel_llm1_llm2_Input --> 0b01139db5ed4587ad37964e3a40c0ec;
	0b01139db5ed4587ad37964e3a40c0ec --> Parallel_llm1_llm2_Output;
	Parallel_llm1_llm2_Input --> a98d4b56bd294156a651230b9293347f;
	a98d4b56bd294156a651230b9293347f --> Parallel_llm1_llm2_Output;
	Parallel_total_chars_Input --> Lambda;
	Lambda --> Parallel_total_chars_Output;
	Parallel_total_chars_Input --> Passthrough;
	Passthrough --> Parallel_total_chars_Output;
	Parallel_llm1_llm2_Output --> Parallel_total_chars_Input;

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After

graph TD;
	Parallel_llm1_llm2_Input --> fake_llm_1;
	fake_llm_1 --> Parallel_llm1_llm2_Output;
	Parallel_llm1_llm2_Input --> fake_llm_2;
	fake_llm_2 --> Parallel_llm1_llm2_Output;
	Parallel_total_chars_Input --> Lambda;
	Lambda --> Parallel_total_chars_Output;
	Parallel_total_chars_Input --> Passthrough;
	Passthrough --> Parallel_total_chars_Output;
	Parallel_llm1_llm2_Output --> Parallel_total_chars_Input;

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Name	Status	Preview	Comments	Updated (UTC)
langchain	⬜️ Ignored (Inspect)	Visit Preview		Oct 31, 2024 6:25pm

[vbarda]

@antwhite thanks for your contribution! could you please add a test for this?

[antwhite]

@vbarda tests added in 2003ad5 . Thanks!