opinionated python configparser library override to deal with configuration variants (PROD, DEV...) and jija2 interpolation
Project description
What is it?
This is an opinionated Python2/Python3 thin layer over the Python configparser library to deal with:
- configuration variants (PROD, DEV...) expressed as alternative keys in ini file
- jinja2 as (optional) interpolation method for configuration values
For Python2, we use Python3 configparser backport.
Concepts
Configuration variants
Basic
With this example:
[group1]
debug=0
debug[DEV]=1
We have two default configuration variant for the debug
key: the DEV
one and the default one.
If you don't do anything special, the debug
value will be 0
(standard default value).
But if you initialize the library with DEV
as configuration name, the debug
value will be 1
.
Now, if you use PROD
as configuration name, as there is no debug[PROD]
line/variant,
the debug value will fallback to standard value: 0
(in this example).
Inheritance
Still with the same example:
[group1]
debug=0
debug[DEV]=1
What about if we use DEV_JOHN_MONDAY
as configuration name when initializing the library?
As there is no debug[DEV_JOHN_MONDAY]
line,
one might think that the retained value would be the default one: 0
.
In fact, the retrained value will be 1
! Why? Because _
(underscore) has a special meaning
in configuration names. This is a kind of inheritance mark.
So DEV_JOHN_MONDAY
means as a configuration name:
- use
DEV_JOHN_MONDAY
if there is a variant with this exact name - (else) use
DEV_JOHN
(first level of inheritance) if there is a variant with this name:DEV_JOHN
- (else) use
DEV
(second level of inheritance) if there is a variant with this name:DEV
- (else) use standard/default value
So with this example:
[group1]
debug=0
debug[DEV]=1
debug[DEV_JOHN]=2
debug[DEV_PETER]=3
debug[DEV_JOHN_MONDAY]=4
debug[DEV_JOHN_TUESDAY]=5
debug[QA]=6
We get this table:
Configuration name | selected value for debug key |
comment |
---|---|---|
FOO |
0 |
standard value is used |
DEV |
1 |
exact variant |
DEV_JOHN_MONDAY |
4 |
exact variant |
DEV_JOHN_FRIDAY |
2 |
DEV_JOHN level of inheritance is used |
DEV_PETER |
3 |
exact variant |
DEV_KATE |
1 |
DEV level of inheritance is used |
DEV_SMITH_FOO_BAR_1 |
1 |
DEV level of inheritance is used |
DEV_JOHN_QA |
2 |
DEV_JOHN level of inheritance is used |
FOO_QA |
0 |
the QA level can be used only if the configuration name begins with QA |
QA5 |
0 |
the QA5 variant does not exist and there is no inheritance because there is no underscore |
QA_5 |
6 |
QA level of inheritance |
jinja2 usage inside configuration values
By default, we use jinja2 as interpolation method for configuration values. The Jinja2 context is initialized with environment variables.
So with this example:
[group1]
key=This is a Jinja2 test value: {% raw %}{{HOME}}{% endraw %}
You will get the {% raw %}{{HOME}}{% endraw %}
placeholder replaced by the corresponding environment variable value.
Missing variables will be replaced by the empty string (without errors).
You can define your own Jinja2 context by adding interpolation=opinionated_configparser.Jinja2Interpolation(jinja2_context)
to the OpinionatedConfigParser
constructor call.
Usage
opinionated_configparser
is just a thin layer over Python configparser library. So you use it exactly in the same way.
Just an example:
from opinionated_configparser import OpinionatedConfigParser
TEST_DICT = {
"section1": {
"key1": "value1",
"key1[foo]": "value2",
"key1[foo_bar]": "value3",
"key2": "value4"
},
"section2": {
"key3": "value5"
}
}
parser = OpinionatedConfigParser(configuration_name="foo")
parser.read_dict(TEST_DICT)
# will output: value2
print(parser.get("section1", "key1"))
# [...]
# use the parser object exactly as configparser.ConfigParser one
# [...]
FAQ
What about if I don't want to use Jinja2 as interpolation method?
Just pass interpolation=None
keyword argument in OpinionatedConfigParser
constructor.
Or use interpolation=configparser.BasicInterpolation()
to get the default
interpolation method of configparser
API.
What about if I want to use different jinja2 template options?
Just pass interpolation=opinionated_configparser.Jinja2Interpolation(jinja2_context, **jinja2_template_kwargs)
keyword argument in OpinionatedConfigParser
constructor.
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