Nox

Standard library

nox.yaml

Parse and write a practical subset of YAML — enough for configuration files. The parser is written in Nox and rejects anything outside the supported subset with a YamlError instead of guessing.

Text
import nox.yaml
from nox.yaml import YamlValue, YamlError

Capability: none. The module works on text; read files with nox.fs.

Functions#

Function Description
parse(text) parses one document into a YamlValue; raises YamlError
get(root, dotted_path) follows a dotted path through nested mappings ("nested.deep"); raises YamlError if a segment is missing. Index sequences through .arr[i]
dump(v) writes a mapping or sequence as block-style YAML
is_string(v), is_int(v), is_float(v), is_bool(v), is_null(v), is_sequence(v), is_mapping(v) kind tests

YamlValue#

Kind Field Type
string s str
integer i int
float f float
boolean b bool
null — —
sequence arr list[YamlValue]
mapping mapping dict[str, YamlValue] (keys are always strings)

Plain scalars are converted automatically: 36 is an integer, 1.5 a float, true/false booleans, null a null; anything else is a string. Quote a value ("36") to force a string.

Nox
import nox.yaml
from nox.yaml import YamlValue, YamlError

y: YamlValue = nox.yaml.parse("name: ada\nage: 36\nlangs:\n  - nox\n  - zig\nnested:\n  deep: true\n  ratio: 1.5\nnothing: null\n")
print(nox.yaml.is_mapping(y), nox.yaml.get(y, "name").s, nox.yaml.get(y, "age").i, nox.yaml.get(y, "nested.deep").b, nox.yaml.is_null(nox.yaml.get(y, "nothing")))
langs: YamlValue = nox.yaml.get(y, "langs")
print(nox.yaml.is_sequence(langs), len(langs.arr), langs.arr[0].s)
print(nox.yaml.dump(y))
try:
    nox.yaml.get(y, "missing")
except YamlError as e:
    print("missing key")
Output
True ada 36 True True
True 2 nox
name: "ada"
age: 36
langs:
  - "nox"
  - "zig"
nested:
  deep: true
  ratio: 1.5
nothing: null

missing key

Supported YAML#

Supported: block mappings and sequences with nesting by indentation (including - key: value items), flow sequences and mappings ([1, 2], {a: 1}), plain, single- and double-quoted scalars, full-line comments, blank lines, and one optional leading ---.

Not supported: trailing (same-line) comments, anchors and aliases (&/*), tags (!!str), merge keys (<<), block scalars (|, >), multiple documents (a second --- or ... raises YamlError), non-string mapping keys and explicit keys (? key).

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