chkit-py

A Python port of chkit — ClickHouse schema management and migration toolkit, written in strict, imperative Python.

Install

pip install chkit-py
chkit --help

The package is named chkit-py on PyPI; the import name is chkit.

Design

• Type safety first. Every public surface is annotated. Ships clean under mypy --strict and pyright strict mode.
• Pydantic v2 models. Runtime validation, frozen, extra="forbid".
• Imperative core. Pure functions over data; minimal classes outside of Pydantic models and the CLI shell.
• No magic. No dynamic imports, no runtime introspection of user code beyond what Pydantic provides.

Layout

src/chkit/
  core/          Schema DSL, diff engine, planner, SQL rendering, validation
  clickhouse/    ClickHouse client wrapper
  cli/           Typer-based CLI (init, generate, migrate, status, check, drift)

Quickstart

In a fresh project:

pip install chkit-py
chkit init                           # scaffold clickhouse.config.py + example schema
chkit generate --name init           # diff schema vs snapshot -> writes migrations/*.sql
chkit migrate --apply                # apply pending, journal in ClickHouse _chkit_migrations
chkit status                         # show applied / pending counts
chkit check --strict                 # CI gate (pending, drift, checksum)
chkit drift                          # snapshot vs current schema diff

clickhouse.config.py reads its credentials from os.environ.get(...) by default. Set CLICKHOUSE_URL, CLICKHOUSE_USER, CLICKHOUSE_PASSWORD, CLICKHOUSE_DB (or override directly in the config).

TypeScript parity

This port matches the upstream TypeScript chkit on every user-facing surface: schema DSL, canonicalization + diff + planner pipeline, codec parser/renderer, validation, all CLI commands, the plugin runtime + its hooks, and every first-party plugin. The journal lives in the same ClickHouse _chkit_migrations table as the TS version, so both implementations can share a database without divergence.

Covered — 1:1 with TS:

• chkit.core — model, canonicalization, codec, planner, validation, snapshot, SQL rendering, apply_on_cluster_to_plan. Includes the Dictionary primitive (dictionary() — full lifecycle: DSL, validation, diff/replace planning, --rename-dictionary, pull introspection, codegen), index-only projections, and function expressions in primaryKey/orderBy.
• All CLI commands: init, generate, migrate, status, check, drift (with live-DB compare), pull, query, plugin. Codegen runs automatically after chkit generate when the plugin is registered (via the on_plan_created hook).
• Flag surface — --rename-table / --rename-column, --table <selector> on generate/migrate/status/check/drift, --dryrun / --json / --config, --strict, --apply / --execute / --allow-destructive (exit code 3 when blocked).
• Plugin runtime + all hooks (on_config_loaded, on_schema_loaded, on_plan_created, on_before_apply, on_after_apply, on_check, on_check_report, on_before_plugin_command, on_pull_introspect, on_init, on_complete).
• First-party plugins: chkit_plugin_codegen (Pydantic model generator, including dictionary attribute models), chkit_plugin_obsessiondb (auth, service management, remote executor, backfill routing, Shared*-engine rewrites), chkit_plugin_backfill (full chunking + execution engine: smart size-aware chunk planning, async submit/poll execution loop with checkpoint + resume, mv_replay detection, and the managed-job submit path via ObsessionDB).
• Journal — _chkit_migrations table (schema + CHKIT_JOURNAL_TABLE override + checksum mismatch detection), per-operation async tracking, INSERT race condition retry, ON CLUSTER + ReplicatedReplacingMergeTree engine when cluster mode is enabled.
• ON CLUSTER <name> support — set clickhouse.cluster and every generated DDL statement is stamped as a final plan post-pass.

Not ported by design — Python convention or ecosystem difference:

• chkit skills proxy (no npx analogue), create-chkit separate scaffolder (use chkit init --example <name> instead), deps.ts auto-install (Python convention is explicit pip install), internal-plugins/skill-hint AI-agent detection.

See DRIFT.md for the append-only decision log covering every port choice, known limitation, and won't-port item.

Development

git clone https://github.com/obsessiondb/chkit
cd chkit_python
python -m venv .venv
.venv\Scripts\python.exe -m pip install -e ".[dev]"
.venv\Scripts\python.exe -m pytest
.venv\Scripts\python.exe -m mypy src
.venv\Scripts\python.exe -m ruff check src tests

Tests under tests/test_*_parity.py and tests/test_sql_validation_e2e.py are direct ports of the TS suites in packages/core/src/*.test.ts. The E2E suite requires a reachable ClickHouse (defaults to http://localhost:8123 with no password — matches a fresh docker run of clickhouse-server). Override via CLICKHOUSE_URL / CLICKHOUSE_PASSWORD.