Package: metayaml
Mata Yaml is several enhancements for yaml format that allow the following:include one yaml file from anotheruse python expression and other fields in the file as valueInclude files syntaxTo include one file or files the ‘extend’ key is used. For example:base.yaml:extend:
  - file1.yaml
  - file2.yaml
name: base.yaml
b: overridden_by_base
new: newfile1.yaml:a: a
b: b
c: c
name: file1.yamlfile2.yaml:a: aa
b: bb
d: d
name: file2.yamlThe order and sequence of file processing is shown in the following table:StepActionIntermediate dict1Read base.yaml and extract extend key{"extend":
    ["file1.yaml", "file2.yaml"] }2Read file1.yaml{
   "a": "a",
   "b": "b",
   "c": "c",
   "name": "file1.yaml"
}3Read file2.yaml and merge/override values{
   "a": "aa", # overridden
   "b": "b",  # overridden
   "c": "c",
   "d": "d",  # added
   "name": "file2.yaml" # overridden
}4Read rest values from base.yaml and
merge/override{
   "a": "aa",
   "b": "overridden_by_base",  # overridden
   "c": "c",
   "d": "d",
   "name": "base.yaml" # overridden
   "new": "new" # added
}Expression syntaxMetayaml supports any python valid expression. For this expression should be enclosed in brackets ${} or $().
The first brackets is used for eager substitute and $() for laze. I.e. expressions in $() are applied after
full read file and its include files but ${} during file read.The access to other values from expression can be done by using dictionary syntax or ‘dash dictionary syntax’.Examples:base.yamlextend:
  - f1.yaml

hour: ${60*60}  # just simple python expression
${2+2}: four  # expression can be in the key
delay: ${hour*2}  # delay is two hour or 7200 seconds
loggers:
  metayaml:
    name: metayaml
    level: debug
    console: false
  backend:
    name: backend
    level: ${loggers.metayaml.level}
    console: ${loggers.metayaml.console}
  ext: ${loggers.metayaml}  # copy whole dict from loggers.metayaml this key

  incorrect: ${delay} ${loggers.ext}  # In this case string representation of objects will be concatenatedf1.yamlrun_interval: $(hour*5)  # 5 hours. But 'hour' is not defined when this file is processed.
                         # Therefore only $() brackets can be used here.InstallationMeta Yaml is in PyPI, so it can be installed directly using:$ pip install metayamlOr from BitBucket:$ git clone https://bitbucket.org/atagunov/metayaml
$ cd metayaml
$ python setup.py installDocumentationDocumentation (such that it is) is available athttps://bitbucket.org/atagunov/metayamlUsagefrom 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.yamlextend:
  - ${join(env["HOME"], ".metayaml", "localconfig.yaml")} # added reading local config from $HOME
user_name: ${env["USER"]}
email: ${user_name + "@example.com"}
debug: falsetest.yamldebug: trueOrder of substitutionThe 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: 1But the following The result is ok:A: 1
B: ${A+1}
AA: ${B}Change merge behaviorBy 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 examplebase.yaml:main:
    iso_3166:
      China: CN
      Honduras: HN
      Madagascar: MG

    country_codes:
      - CN
      - HN
      - MG

    country_codes_3:
      - CHN
      - HND
      - MDGlast.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 methodThere 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
  # - 5.5.5.5Inherit methodThere 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: 3LicenseMetaYaml is released under a MIT license.