pyyaml-future

Use YAML 1.3 Features in PyYAML (YAML 1.1)

Synopsis

import yaml
from yamlfuture import Loader

# Define your own anchors:
Loader.anchors = {'name': 'YAML'}
# !import relative to this:
Loader.filepath = __file__

yamlstream = """\
---
greeting: !+ |
  Hello {*name}.
  Welcome to the future!

copyright: !import [../data.yaml, /copyright/year]
"""

print(yaml.dump(yaml.load(yamlstream, Loader))

Status

This module is very ALPHA.

YAML 1.3 is still being defined. As the various features of the YAML 1.3 evolve, yamlfuture will evolve.

Use with caution for now.

Description

YAML 1.3 is bringing exciting new features to YAML (while keeping the YAML you know and love (or hate) the same).

This package lets you use the new features (or close approximations) in PyYAML now.

This is a very early release. More features and documentation coming soon.

Features

YAML 1.3 adds optional "language features" that you can request that a parser use. Some of the planned ones are:

Standard Library node functions:

- @merge(*base)
  foo: 42
- stuff: @import stuff.yaml

String expansion (interpolation):
```
greeting: `Hello {*name}`
```
Extended aliases with YPath:
```
total: @sum(*nums/x, $*nums/y)
```

In current PyYAML we can emulate these with tags and implicit typing, as long as we don't use invalid YAML 1.1 syntax.

For @func(1,2) we use !func [1,2]

For *alias/path/value we use +*alias/path/value.

For interpolation we use !+ Hello {*name} instead of backticks.

YAML 1.3 actually parses these new things into the same event model. In other words, a 1.3 parser would report @foo(*bar,42) as !foo [*bar, 42]. Just with a cleaner syntax.

yamlfuture current features

Merge a sequence of mappings:

merged: !merge [*map1, *map2, foo: bar]

Define anchors (from Python) outside the YAML stream:

Loader.anchors = {"name": "world"}
yaml.load("hello: *name", Loader)

Use aliases with paths:

value: &foo
  yaml: future
when: +*foo/yaml
absolute: +*/foo/0/bar
siblings:
  a: 2
  b: 4
  all: [+*:a, +*:b]
foo: { bar: +*../../siblings/a }

String interpolation:
```
greeting: !+ Hello {*name}!
```

Import other YAML files into any node:

foo: !import foo.yaml
bar: !import [foo.yaml, /0/bar]

Import/render external "template" yaml files:

# file 'template.yaml'
foo:
  bar: *value

# file 'main.yaml'
bar: !render [template.yaml, value: baz]

License & Copyright

This project is licensed under the terms of the MIT license. See LICENSE for more details.

yaml / pyyaml-future