Configure your program via environment variables, validated by pydantic.
Project description
Umwelt
Describe a configuration schema with dataclasses or pydantic and load values from the environment, in a static-typing-friendly way.
Examples
Flat
>>> os.environ["APP_HOSTS"] = '["b.org","sky.net"]'
>>> os.environ["APP_TOKEN"] = "very secret"
from typing import Sequence
from pydantic import SecretStr
import umwelt
class MyConfig:
hosts: Sequence[str]
token: SecretStr
replicas: int = 2
config = umwelt.new(MyConfig, prefix="app")
>>> dataclasses.is_dataclass(config)
True
>>> config.hosts
["b.org", "sky.net"]
>>> config.token
SecretStr('**********')
>>> config.replicas
2
Nested
>>> os.environ["APP_DB_PORT"] = "32"
from __future__ import annotations # for forward-references
from pydantic import UrlStr
import umwelt
class MyConfig:
db: DbConfig
host: UrlStr = "http://b.org"
@umwelt.subconfig
class DbConfig:
port: int
debug: bool = False
config = umwelt.new(MyConfig, prefix="app")
>>> config.host
"http://b.org"
>>> config.db.port
32
Install
$ pip install umwelt
Features
umwelt.new
umwelt.new
expects one positional argument: the config class to fill.
Umwelt will convert it into a dataclass if it's not one already.
umwelt.new
also accepts named arguments:
source
(by defaultos.environ
) is aMapping[str, str]
from which values are extracted.prefix
can be a string or a callable. As a string, it is prepended to the config field's name. As a callable, it receives the config field's name and its result is the source key name.decoder
is a callable expecting a type and a string, and returns a conversion of that string in that type, or in a type that pydantic can convert in that type. For example, when umwelt's defaultdecoder
is called with (List[Set[int]]
,"[[1]]"
), it simply decodes the string from JSON and hence returns a list of lists, which pydantic properly converts into a list of sets.
@umwelt.subconfig
@umwelt.subconfig
tags classes so that, when they appear as field annotations
in another config class, umwelt.new
doesn't instantiate them from a single
source
value, but rather from one source
value per class field.
Example:
class Point: # no @subconfig
def __init__(self, s: str): # string input
self.x, self.y = s.split(",", 1) # arbitrary implementation
class MyConf:
point: Point
conf = umwelt.new(MyConf, source={"POINT": "1,2"}) # one source entry
conf.point # <Point at 0x7f07b1d04750>
conf.point
is an instance of Point, built by passing the input value "1,2"
directly to Point.__new__
.
There is only one source
key: POINT
.
Now compare with @umwelt.subconfig
:
@umwelt.subconfig
class Point:
x: int
y: int
class MyConf:
point: Point
conf = umwelt.new(MyConf, source={"POINT_X": "1", "POINT_Y": "2"})
conf.point # Point(x=1, y=2)
conf.point
is still an instance of Point (Point has been made a
dataclass by Umwelt, hence the automatic __str__
implementation).
There are two source
keys: POINT_X
and POINT_Y
, each corresponding to
a field of the Point class.
Comparison with Ecological
I've used Ecological for a long time. Today, a large part of Ecological's codebase implements features already found in dataclasses and pydantic, which are more mature. I believe Ecological's design can be dramatically simplified and improved by enforcing a strict separation of concerns:
- class scaffolding is the responsibility of dataclasses (which, compared
to metaclasses, is simpler, more introspectable, and comes with helpers like
asdict
); - type coercion and validation is the responsibility of pydantic (which has more features, e.g. nested data types, JSON Schema, serialization, etc.);
- mapping a pydantic schema (the configuration class) to a string-to-string
dict (like
os.environ
) is the responsibility of Umwelt.
Some compatibility-breaking decisions prevent from doing this in Ecological:
- Don't autoload configuration values, especially not at class definition time.
Instead, offer just one function (
umwelt.new
) that loads the configuration when it is called. - Don't tie variable prefixes to configuration classes, as that doesn't play well with nested configurations.
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