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TL;DR
# config.yml
foo:
bar: <% ENV[REQUIRED] %>
baz: <% ENV[OPTIONAL, true] %>
list_of_stuff:
- fun<% ENV[NICE, dament] %>al
- fun<% ENV[AGH, er] %>al
- more/<% ENV[THAN, er] %>/one/<% ENV[interpolation, er] %>!
# app.py
config = Config.from_yaml('config.yml')
print(config.foo.bar)
print(config.foo['baz'])
for item in config.list_of_stuff:
print(item)
pip install configly[yaml]
Introduction
Loading configuration is done in every (application) project, and yet it is often overlooked and condidered too easy or straightforward to bother using a library to manage doing it.
Therefore, we often see code like this:
# config.py
import os
# Maybe it's following 12factor and loading all the config from the environment.
config = {
'log_level': os.getenv('LOG_LEVEL'),
'database': {
# At least here, I can nest values if I want to organize things.
'password': os.environ['DATABASE_PASSWORD'],
'port': int(os.environ['DATABASE_PORT']),
}
}
or this
# config.py
import os
class Config:
log_level = os.getenv('LOG_LEVEL')
# Here it's not so easy to namespace
database_password = os.environ['DATABASE_PASSWORD']
database_port = int(os.environ['DATABASE_PORT'])
# Oh goodness!
class DevConfig(Config):
environment = 'dev'
or this
import configparser
# ...🤢... Okay I dont even want to get into this one.
And this is all assuming that everyone is loading configuration at the outermost entrypoint! The two worst possible outcomes in configuration are:
- You are loading configuration lazily and/or deeply within your application, such that it hits a critical failure after having seemingly successfully started up.
- There is not a singular location at which you can go to see all configuration your app might possibly be reading from.
The pitch
Configly
asserts configuration should:
- Be centralized
- One should be able to look at one file to see all (env vars, files, etc) which must exist for the application to function.
- Be comprehensive
- One should not find configuration being loaded secretly elsewhere
- Be declarative/static
- code-execution (e.g. the class above) in the definition of the config inevitably makes it hard to interpret, as the config becomes more complex.
- Be namespacable
- One should not have to prepend
foo_
namespaces to allfoo
related config names
- One should not have to prepend
- Be loaded, once, at app startup
- (At least the definition of the configuration you're loading)
- (Ideally) have structured output
- If something is an
int
, ideally it would be read as an int.
- If something is an
To that end, the configly.Config
class exposes a series of classmethods from which your config
can be loaded. It's largely unimportant what the input format is, but we started with formats
that deserialize into at least str
, float
, int
, bool
and None
types.
# Currently supported input formats.
config = Config.from_yaml('config.yml')
config = Config.from_json('config.json')
config = Config.from_toml('config.toml')
Given an input config.yml
file:
# config.yml
foo:
bar: <% ENV[REQUIRED] %>
baz: <% ENV[OPTIONAL, true] %>
list_of_stuff:
- fun<% ENV[NICE, dament] %>al
- fun<% ENV[AGH, er] %>al
- more/<% ENV[THAN, er] %>/one/<% ENV[interpolation, er] %>!
A number of things are exemplified in the example above:
-
Each
<% ... %>
section indicates an interpolated value, the interpolation can be a fragment of the overall value, and multiple values can be interpolated within a single value. -
ENV
is an "interpolator" which knows how to obtain environment variables -
[VAR]
Will raise an error if that piece of config is not found, whereas[VAR, true]
will defaultVAR
to the value after the comma -
Whatever the final value is, it's interpreted as a literal value in the format of the file which loads it. I.E.
true
-> pythonTrue
,1
-> python1
, andnull
-> pythonNone
.
Now that you've loaded the above configuration:
# app.py
config = Config.from_yaml('config.yml')
# You can access namespaced config using dot access
print(config.foo.bar)
# You have use index syntax for dynamic, or non-attribute-safe key values.
print(config.foo['baz'])
# You can iterate over lists
for item in config.list_of_stuff:
print(item)
# You can *generally* treat key-value maps as dicts
for key, value in config.foo.items():
print(key, value)
# You can *actually* turn key-value maps into dicts
dict(config.foo) == config.foo.to_dict()
Installing
# Basic installation
pip install configly
# To use the yaml config loader
pip install configly[yaml]
# To use the toml config loader
pip install configly[toml]
# To use the vault config loader
pip install configly[vault]
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