simplified environment variable parsing
Project description
environs: simplified environment variable parsing
Environs is a Python library for parsing environment variables.
Environs is inspired by envparse and uses marshmallow under the hood for validating, deserializing, and serializing values.
Install
pip install environs
Basic usage
# export GITHUB_USER=sloria
# export API_KEY=123abc
# export SHIP_DATE='1984-06-25'
# export ENABLE_LOGIN=true
# export GITHUB_REPOS=webargs,konch,ped
# export COORDINATES=23.3,50.0
from environs import Env
env = Env()
# reading an environment variable
gh_user = env('GITHUB_USER') # => 'sloria'
secret = env('SECRET') # => raises error if not set
# casting
api_key = env.str('API_KEY') # => '123abc'
date = env.date('SHIP_DATE') # => datetime.date(1984, 6, 25)
# providing a default value
enable_login = env.bool('ENABLE_LOGIN', False) # => True
enable_feature_x = env.bool('ENABLE_FEATURE_X', False) # => False
# parsing lists
gh_repos = env.list('GITHUB_REPOS') # => ['webargs', 'konch', 'ped']
coords = env.list('COORDINATES', subcast=float) # => [23.3, 50.0]Supported types
The following are all type-casting methods of Env:
env.str
env.bool
env.int
env.float
env.decimal
env.list (accepts optional subcast keyword argument)
env.dict (accepts optional subcast keyword argument)
env.json
env.datetime
env.date
env.timedelta (assumes value is an integer in seconds)
env.uuid
Handling prefixes
# export MYAPP_HOST=lolcathost
# export MYAPP_PORT=3000
with env.prefixed('MYAPP_'):
host = env('HOST', 'localhost') # => 'lolcathost'
port = env.int('PORT', 5000) # => 3000Validation
# export TTL=-2
# export NODE_ENV='invalid'
# export EMAIL='^_^'
# simple validator
env.int('TTL', validate=lambda n: n > 0)
# => Environment variable "TTL" invalid: ['Invalid value.']
# using marshmallow validators
from marshmallow.validate import OneOf
env.str('NODE_ENV',
validate=OneOf(['production', 'development'],
error='NODE_ENV must be one of: {choices}'))
# => Environment variable "NODE_ENV" invalid: ['NODE_ENV must be one of: production, development']
# multiple validators
from marshmallow.validate import Length, Email
env.str('EMAIL', validate=[Length(min=4), Email()])
# => Environment variable "EMAIL" invalid: ['Shorter than minimum length 4.', 'Not a valid email address.']Serialization
# serialize to a dictionary of simple types (numbers and strings)
env.dump()
# { 'API_KEY': '123abc',
# 'COORDINATES': [23.3, 50.0],
# 'ENABLE_FEATURE_X': False,
# 'ENABLE_LOGIN': True,
# 'GITHUB_REPOS': ['webargs', 'konch', 'ped'],
# 'GITHUB_USER': 'sloria',
# 'MYAPP_HOST': 'lolcathost',
# 'MYAPP_PORT': 3000,
# 'SHIP_DATE': '1984-06-25'}Defining custom parser behavior
# export DOMAIN='http://myapp.com'
# export COLOR=invalid
from furl import furl
# Register a new parser method for paths
@env.parser_for('furl')
def furl_parser(value):
return furl(value)
domain = env.furl('DOMAIN') # => furl('https://myapp.com')
# Custom parsers can take extra keyword arguments
@env.parser_for('enum')
def enum_parser(value, choices):
if value not in choices:
raise environs.EnvError('Invalid!')
return value
color = env.enum('COLOR', choices=['black']) # => raises EnvErrorNote: Environment variables parsed with a custom parser function will be serialized by Env.dump without any modification. To define special serialization behavior, use Env.parser_from_field instead (see next section).
Marshmallow integration
# export STATIC_PATH='app/static'
# Custom parsers can be defined as marshmallow Fields
import pathlib
import marshmallow as ma
class PathField(ma.fields.Field):
def _deserialize(self, value, *args, **kwargs):
return pathlib.Path(value)
def _serialize(self, value, *args, **kwargs):
return str(value)
env.add_parser_from_field('path', PathField)
static_path = env.path('STATIC_PATH') # => PosixPath('app/static')
env.dump()['STATIC_PATH'] # => 'app/static'FAQ
Why envvars?
See The 12-factor App section on configuration.
Why not os.environ?
While os.environ is enough for simple use cases, a typical application will need a way to manipulate and validate raw environment variables. Environs abstracts common tasks for handling environment variables.
Environs will help you
cast envvars to the correct type
specify required envvars
define default values
validate envvars
parse strings into lists and dicts
parse dates, datetimes, and timedeltas
serialize your configuration to JSON, YAML, etc.
Why another library?
There are many great Python libraries for parsing environment variables. In fact, most of the credit for environs’ public API goes to the authors of envparse and django-environ.
environs aims to meet two additional goals:
Make it easy to extend parsing behavior and develop plugins.
Leverage the deserialization and validation functionality provided by a separate library (marshmallow).
License
MIT licensed. See the LICENSE file for more details.
Changelog
0.1.0 (2016-04-25)
First PyPI release.
Release history Release notifications | RSS feed
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