Mata Yaml is several enhancements for yaml format that allow the following:
include one yaml file from another
use python expression and other fields in the file as value
Include files syntax
To 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: new
file1.yaml:
a: a b: b c: c name: file1.yaml
file2.yaml:
a: aa b: bb d: d name: file2.yaml
The order and sequence of file processing is shown in the following table:
Step |
Action |
Intermediate dict |
|---|---|---|
1 |
Read base.yaml and extract extend key |
{"extend":
["file1.yaml", "file2.yaml"] }
|
2 |
Read file1.yaml |
{
"a": "a",
"b": "b",
"c": "c",
"name": "file1.yaml"
}
|
3 |
Read file2.yaml and merge/override values |
{
"a": "aa", # overridden
"b": "b", # overridden
"c": "c",
"d": "d", # added
"name": "file2.yaml" # overridden
}
|
4 |
Read 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 syntax
Metayaml 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.yaml
extend:
- 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 concatenated
f1.yaml
run_interval: $(hour*5) # 5 hours. But 'hour' is not defined when this file is processed.
# Therefore only $() brackets can be used here.
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.
1 maintainer
Release files for metayaml 1.2
For a detailed explanation of source distributions (sdists) and built distributions (wheels), please see the package formats documentation.
Source distribution (sdist)
| File | Size | Uploaded | |
|---|---|---|---|
| metayaml-1.2.tar.gz | 10.2 kB | Details |
Release files / metayaml-1.2.tar.gz
| Download URL | metayaml-1.2.tar.gz |
|---|---|
| Size | 10.2 kB |
| Tags | Source |
|
SHA-256 checksum How to use checksums |
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|
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