Why only two runtime dependencies

open-meteo-client has exactly two runtime dependencies: httpx and pydantic.

It doesn’t use:

  • requests — httpx supersedes it for new code (async support, HTTP/2, connection pooling semantics).

  • aiohttp — httpx covers the same ground with a cleaner API.

  • flatbuffers — Open-Meteo offers a FlatBuffers wire format, but JSON is fine for our scale and dramatically simpler to debug.

  • pandas / numpy — would dwarf the library’s own footprint, and the audience for today("Dresden") doesn’t need a DataFrame.

The shape of “lightweight”

Dimension

Target

Install size

under 20 MB including transitive deps

Import time

under 100 ms cold

Deps to pin in your requirements.txt

2

Security surface

as small as practical

Where this matters

  • AWS Lambda / serverless — every MB and every ms of cold start counts.

  • Home automation (Home Assistant, openHAB) — run on SBCs with modest memory.

  • CLI tools — import time directly hits UX.

Where it doesn’t

  • Data-science notebooks where you already have pandas loaded.

  • Long-running services where import time is a one-time cost.

We’re optimizing for the first group.