run_flow_from_json in Depth

Where we left off

Beginner used run_flow_from_json as a black box: hand it a flow.json and an input_value, get an answer back. It has one more feature worth knowing before Intermediate moves on to the REST API: tweaks, overriding a component's field for a single run without editing the flow.json file on disk.

Why this matters

A shipped flow.json is meant to be a stable, reviewable artifact, exactly like a config file. Editing it every time you want to try a different system prompt defeats that. tweaks gives you the same one-off override you'd get from typing into a component's field on the canvas and clicking Run, but from code, scriptable, and without ever touching the file.

Do this yourself

1. Open flow.json in this folder (or reopen the Lesson 2 flow, they're the same shape: Chat Input -> Google Generative AI -> Chat Output).
2. Find the Google Generative AI component's System Message field in the canvas, type something like "Answer only in pirate speak", run it in the Playground, confirm the tone changes.
3. Clear that field back out. The tweaks dict in lesson.py does the exact same override, but only for one Python call, the file (and the canvas, if you reload it) goes right back to its original system message afterward.

The code, piece by piece

GEMINI_COMPONENT_ID = "GoogleGenerativeAIComponent-lesson10"
gemini._id = GEMINI_COMPONENT_ID

tweaks targets a component by its id, the same id visible in flow.json's data.nodes[].id. Every component gets a random suffix by default (GoogleGenerativeAIComponent-a2YHI, different every time you build the graph), so this lesson pins a fixed, readable id right after constructing the component, before wiring it into anything, so the id in flow.json matches the id used in tweaks below.

run_flow_from_json(
    flow=str(FLOW_PATH),
    input_value=question,
    tweaks={GEMINI_COMPONENT_ID: {"system_message": "Answer only in pirate speak."}},
)

The dict's keys are component ids, its values are {field_name: new_value} overrides for that component. Any field the component has can be tweaked this way, not just system_message, model_name or temperature work exactly the same. The override only applies to this one run_flow_from_json call, flow.json on disk is never modified.