Installation

Meta Yaml is in PyPI, so it can be installed directly using:

$ pip install metayaml

Or from BitBucket:

$ git clone https://bitbucket.org/atagunov/metayaml
$ cd metayaml
$ python setup.py install

Documentation

Documentation (such that it is) is available at https://bitbucket.org/atagunov/metayaml

Usage

from metayaml import read
read(["config.yaml",
      "test.yaml"],
     {'join': os.path.join, # allows get right os specific path in yaml file
      'env': os.environ}  # allows use system environments from yaml file
    )

config.yaml

extend:
  - ${join(env["HOME"], ".metayaml", "localconfig.yaml")} # added reading local config from $HOME
user_name: ${env["USER"]}
email: ${user_name + "@example.com"}
debug: false

test.yaml

debug: true

Order of substitution

The substitutions are done in order of the values in the file. I.e. the following example will be failed:

B: ${A+1}     <--- A is not defined here
AA: ${B}
A: 1

But the following The result is ok:

A: 1
B: ${A+1}
AA: ${B}

Change merge behavior

By default it is possible to add new keys in the dict and replace the list. In some cases it is necessary to remove keys from base file or add some values to list. For example

base.yaml:

main:
    iso_3166:
      China: CN
      Honduras: HN
      Madagascar: MG

    country_codes:
      - CN
      - HN
      - MG

    country_codes_3:
      - CHN
      - HND
      - MDG

last.yaml:

extend:
  - base.yaml
main:
  iso_3166:
     China: ${__del__}  #  key 'China' will be removed from the result
     Liberia: LR  # add new key

  country_codes:
     - LR         # after merge country_codes contains only one element.

  country_codes_3:
    ${__extend__}:
      - LBR       # the result list is ["CHN", "HND", "MDG", "LBR"]

The result of the code:

d = read("last.yaml")
print d

{
    "main": {
        "iso_3166": {
            "Honduras": "HN",
            "Madagascar": "MG",
            "Liberia": "LR"
        },
        "country_codes": [
            "LR"
        ],
        "country_codes_3": [
            "CHN",
            "HND",
            "MDG",
            "LBR"
        ]
    }
}

Copy method

There is method ‘cp’ which copy dict/list with extending:

cron:
  daily:
    min: 0
    hour: 0

  monthly:
    min: 0
    hour: 0
    day: 1

schedule:
  nighttask: ${cp(cron.daily, min=5)}  # min will be replaced to 5
  #  min: 5
  #  hour: 0
  daytask: ${cp(cron.daily, min=7, hour=13)} # min and hour are replaced
  #  min: 7
  #  hour: 13
  monthtask: ${cp(cron.monthly, day=2)}
  #  min: 0
  #  hour: 0
  #  day: 2

deploy:
  subnets:
    - 1.1.1.1
    - 2.2.2.2

  base_elb:
    - 4.4.4.4
    - 5.5.5.5

  elb: ${cp(deploy.subnets, "3.3.3.3", *deploy.base_elb)}
  # - 1.1.1.1
  # - 2.2.2.2
  # - 3.3.3.3
  # - 4.4.4.4
  # - 5.5.5.5

Inherit method

There are another way to copy existed dict and update some fields:

foo:
  bar:
    baz: 1
    buz: 2
    foobar: 3
  foobar: [4, 5]

bar:
  ${__inherit__}: foo.bar  # bar will be replaces by content of for.bar
  buz: 33

# the result value of 'bar' will be
#    baz: 1
#    buz: 33
#    foobar: 3

License

MetaYaml is released under a MIT license.