ktav 0.6.0

Python bindings for Ktav — a plain configuration format. No quotes, no commas, dotted keys.

ktav (Python)

Python bindings for Ktav — a plain configuration format. JSON-shape, no quotes, no commas, dotted keys. Powered by Rust under the hood.

Languages: English · Русский · 简体中文

Specification: this package implements Ktav 0.1. The format is versioned and maintained independently of this package — see ktav-lang/spec for the formal document.

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Install

pip install ktav

Wheels are published for every major platform and every supported Python version:

• Linux (manylinux + musllinux) — x86_64, aarch64
• macOS — x86_64, arm64 (Apple Silicon)
• Windows — x64, arm64

Python 3.9+ is required. The wheels target the stable ABI (abi3-py39), so a single wheel per platform serves every supported CPython release.

If no prebuilt wheel matches your platform, pip falls back to the source distribution and compiles it locally — you need a Rust toolchain (rustup) and the Python development headers.

Quick start

Parse — read typed fields straight off the dict

import ktav

src = """
service: web
port:i 8080
ratio:f 0.75
tls: true
tags: [
    prod
    eu-west-1
]
db.host: primary.internal
db.timeout:i 30
"""

cfg = ktav.loads(src)

service: str = cfg["service"]
port:    int = cfg["port"]
ratio: float = cfg["ratio"]
tls:    bool = cfg["tls"]
tags: list[str] = cfg["tags"]
db_host:    str = cfg["db"]["host"]
db_timeout: int = cfg["db"]["timeout"]

Walk — dispatch on the runtime type

for k, v in cfg.items():
    if v is None:              kind = "null"
    elif isinstance(v, bool):  kind = f"bool={v}"   # bool first — True is also an int!
    elif isinstance(v, int):   kind = f"int={v}"
    elif isinstance(v, float): kind = f"float={v}"
    elif isinstance(v, str):   kind = f"str={v!r}"
    elif isinstance(v, list):  kind = f"array({len(v)})"
    elif isinstance(v, dict):  kind = f"object({len(v)})"
    print(f"{k} -> {kind}")

Build & render — construct a document in code

doc = {
    "name": "frontend",
    "port": 8443,
    "tls": True,
    "ratio": 0.95,
    "upstreams": [
        {"host": "a.example", "port": 1080},
        {"host": "b.example", "port": 1080},
    ],
    "notes": None,
}
text = ktav.dumps(doc)
# name: frontend
# port:i 8443
# tls: true
# ratio:f 0.95
# upstreams: [
#     { host: a.example  port:i 1080 }
#     { host: b.example  port:i 1080 }
# ]
# notes: null

A complete runnable version lives in examples/basic.py.

Four entry points mirror the standard library json module:

Function	Purpose
ktav.loads(s)	Parse a Ktav string (or UTF-8 bytes).
ktav.dumps(obj)	Serialise a native Python value.
ktav.load(fp)	Parse from a file-like object.
ktav.dump(obj, fp)	Serialise to a file-like object.

load / dump accept both text-mode and binary-mode files.

Type mapping

Ktav	Python
null	None
true / false	bool
:i <digits>	int
:f <number>	float
bare scalar	str
[ ... ]	list
{ ... }	dict

Ktav keeps "no magic types" — a bare port: 8080 stays a string at the parser level. Use the typed markers :i / :f when you want numbers, or type-coerce at the application layer.

dict preserves insertion order (Python 3.7+ guarantee), matching the ordered-object semantics of Ktav.

Serialisation is the inverse:

• Python int → :i marker (including arbitrary-precision bigints).
• Python float → :f marker (decimal point always present; NaN / ±Infinity are rejected — Ktav 0.1.0 does not represent them).
• Python tuple is accepted as an array, for symmetry with list.
• Non-str keys in a dict raise KtavEncodeError.

Key escaping

Since spec 0.6.0 a literal . or : inside a key segment is written with a backslash:

a\.b: v        # key is the single segment "a.b" -> {"a.b": "v"}
a\:b: v        # key contains a colon            -> {"a:b": "v"}
x.y\.z: v      # split on the first dot only     -> {"x": {"y.z": "v"}}

A literal backslash in a key is \\.

Errors

import ktav

try:
    ktav.loads("x: [")
except ktav.KtavDecodeError as e:
    print("decode:", e)

try:
    ktav.dumps({"v": float("nan")})
except ktav.KtavEncodeError as e:
    print("encode:", e)

# Catching the base class catches either.
try:
    ktav.loads("a: 1\na: 2")
except ktav.KtavError:
    ...

Exception	Raised by	Base
KtavError	(base)	Exception
KtavDecodeError	loads / load	KtavError
KtavEncodeError	dumps / dump	KtavError

Philosophy

Ktav is intentionally small. Its five design principles (from spec/CONTRIBUTING.md):

1. Locality — a line's meaning does not depend on another line.
2. One sentence — any new rule fits in one sentence of the spec.
3. No whitespace sensitivity (line breaks aside).
4. No magic types — the format never decides "8080" means a number.
5. Explicit over clever — :: is verbose on purpose.

The Python bindings honour this: they add no schema inference, no auto-casting, no defaulting. If you want typing, you do it at the boundary with your own tool — pydantic, dataclasses, attrs — against the native Python structures this library returns.

Other Ktav implementations

• spec — specification + conformance suite
• rust — reference Rust crate (cargo add ktav); these Python bindings are a thin PyO3 wrapper around it
• csharp — C# / .NET (dotnet add package Ktav)
• golang — Go (go get github.com/ktav-lang/golang)
• java — Java / JVM (io.github.ktav-lang:ktav on Maven Central)
• js — JS / TS (npm install @ktav-lang/ktav)
• php — PHP (composer require ktav-lang/ktav)

Versioning

This package follows Semantic Versioning with the pre-1.0 convention that a MINOR bump is breaking. The package version and the ktav crate version move together. ktav.__spec_version__ reports the Ktav format version this binding supports.

Development

See CONTRIBUTING.md for the dev setup, test layout, and the contribution workflow.

Support the project

The author has many ideas that could be broadly useful to IT worldwide — not limited to Ktav. Realizing them requires funding. If you'd like to help, please reach out at [e-mail].

License

MIT OR Apache-2.0. See LICENSE-MIT and LICENSE-APACHE.