environs 1.0.0

simplified environment variable parsing

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)  # => 3000

Proxied variables

# export MAILGUN_LOGIN=sloria
# export SMTP_LOGIN={{MAILGUN_LOGIN}}

smtp_login = env('SMTP_LOGIN')  # =>'sloria'

Validation

# 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 EnvError

Note: 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'

Reading .env files

Use the external read_env package to read .env files into os.environ.

pip install read_env

# myapp/.env
DEBUG=true
PORT=4567

Call read_env before parsing variables.

from environs import Env
from read_env import read_env

env = Env()
# Read .env into os.environ
read_env()

env.bool('DEBUG')  # => True
env.int('PORT')   # => 4567

Why…?

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 list and dict values

• parse dates, datetimes, and timedeltas

• parse proxied variables

• 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 three additional goals:

1. Make it easy to extend parsing behavior and develop plugins.

2. Leverage the deserialization and validation functionality provided by a separate library (marshmallow).

3. Clean up redundant API.

License

MIT licensed. See the LICENSE file for more details.

Changelog

1.0.0 (2016-04-30)

• Support for proxied variables (#2).

• Backwards-incompatible: Remove env.get method. Use env() instead.

• Document how to read .env files (#1).

0.1.0 (2016-04-25)

• First PyPI release.