cbor2

[SoulMelody]

https://pypi.org/project/cbor2/

[ndonkoHenri]

cbor2 1.6.4 is now supported on Android and iOS: https://pypi.flet.dev/cbor2

cbor2 gives you CBOR (RFC 8949) — a binary, schema-less serialization format with the same data model as JSON plus native bytes, big integers, decimals, and tagged types, in a fraction of the size. The API mirrors json: cbor2.dumps / cbor2.loads / dump / load.

Install

Just add it to your dependencies:

[project]
dependencies = [
  "flet",
  "cbor2==6.1.4",
]

Example

Encodes a record JSON can't represent (raw bytes, a 100-bit integer), decodes it back, and shows the size win on screen:

import json

import cbor2
import flet as ft


def main(page: ft.Page):
    page.title = "cbor2 demo"

    record = {
        "id": 7,
        "name": "sensor-α",
        "reading": 21.5,
        "raw": b"\x00\x01\x02\x03",  # bytes are native in CBOR — impossible in JSON
        "big": 2**100,               # >64-bit int → CBOR bignum tag
    }

    payload = cbor2.dumps(record)
    ok = cbor2.loads(payload) == record

    # closest JSON equivalent needs hex/str workarounds:
    json_size = len(json.dumps({**record, "raw": record["raw"].hex(), "big": str(record["big"])}))

    page.add(
        ft.Text(f"cbor2 round-trip {'OK ✅' if ok else 'FAILED ❌'}", weight=ft.FontWeight.BOLD),
        ft.Text(f"CBOR payload: {len(payload)} bytes (JSON equivalent: {json_size} bytes)"),
        ft.Text(f"hex: {payload.hex()[:48]}…", font_family="monospace"),
    )


ft.run(main)

Things to know

• Version context: cbor2 6.x is a Rust rewrite and only ships native wheels — that's why versions ≥ 6.0 don't install in mobile flet builds without this wheel. If you're stuck on an older setup, cbor2==5.7.0 is the last release with a pure-Python py3-none-any wheel that works everywhere — but on mobile that was always the slow pure-Python path, so prefer 6.1.4.
• 6.x behavior change worth knowing when migrating from 5.x: arrays nested inside a CBORTag payload decode as immutable tuples, not lists (loads(dumps(CBORTag(4000, ["x"]))) → .value == ("x",)). Top-level and dict/list nesting still decode as regular lists/dicts.
• Everything runs fully offline — cbor2 is a pure codec: no storage, no config dirs, no network. Encoding/decoding is fast enough that you won't need page.run_thread unless you're processing very large payloads.
• The cbor2 command-line tool that ships with the package is irrelevant on mobile; the library API is the whole story there.