environs is a Python library for parsing environment variables. It allows you to store configuration separate from your code, as per The Twelve-Factor App methodology.
- Features
- Install
- Basic usage
- Supported types
- Reading .env files
- Handling prefixes
- Variable expansion
- Validation
- Deferred validation
- Serialization
- Defining custom parser behavior
- Usage with Flask
- Usage with Django
- Why...?
- License
- Type-casting
- Read
.envfiles intoos.environ(useful for local development) - Validation
- Define custom parser behavior
- Framework-agnostic, but integrates well with Flask and Django
pip install environs With some environment variables set...
export GITHUB_USER=sloria export MAX_CONNECTIONS=100 export SHIP_DATE='1984-06-25'export TTL=42 export ENABLE_LOGIN=true export GITHUB_REPOS=webargs,konch,ped export COORDINATES=23.3,50.0 export LOG_LEVEL=DEBUGParse them with environs...
fromenvironsimportEnvenv=Env() env.read_env() # read .env file, if it exists# required variablesgh_user=env("GITHUB_USER") # => 'sloria'secret=env("SECRET") # => raises error if not set# castingmax_connections=env.int("MAX_CONNECTIONS") # => 100ship_date=env.date("SHIP_DATE") # => datetime.date(1984, 6, 25)ttl=env.timedelta("TTL") # => datetime.timedelta(0, 42)log_level=env.log_level("LOG_LEVEL") # => logging.DEBUG# providing a default valueenable_login=env.bool("ENABLE_LOGIN", False) # => Trueenable_feature_x=env.bool("ENABLE_FEATURE_X", False) # => False# parsing listsgh_repos=env.list("GITHUB_REPOS") # => ['webargs', 'konch', 'ped']coords=env.list("COORDINATES", subcast=float) # => [23.3, 50.0]The following are all type-casting methods of Env:
env.strenv.boolenv.intenv.floatenv.decimalenv.list(accepts optionalsubcastanddelimiterkeyword arguments)env.dict(accepts optionalsubcast_keysandsubcast_valueskeyword arguments)env.jsonenv.datetimeenv.dateenv.timedelta(assumes value is an integer in seconds)env.urlenv.uuidenv.log_levelenv.path(casts to apathlib.Path)
# .env DEBUG=true PORT=4567Call Env.read_env before parsing variables.
fromenvironsimportEnvenv=Env() # Read .env into os.environenv.read_env() env.bool("DEBUG") # => Trueenv.int("PORT") # => 4567By default, Env.read_env will look for a .env file in current directory and (if no .env exists in the CWD) recurse upwards until a .env file is found.
You can also read a specific file:
fromenvironsimportEnvwithopen(".env.test", "w") asfobj: fobj.write("A=foo\n") fobj.write("B=123\n") env=Env() env.read_env(".env.test", recurse=False) assertenv("A") =="foo"assertenv.int("B") ==123# export MYAPP_HOST=lolcathost# export MYAPP_PORT=3000withenv.prefixed("MYAPP_"): host=env("HOST", "localhost") # => 'lolcathost'port=env.int("PORT", 5000) # => 3000# nested prefixes are also supported:# export MYAPP_DB_HOST=lolcathost# export MYAPP_DB_PORT=10101withenv.prefixed("MYAPP_"): withenv.prefixed("DB_"): db_host=env("HOST", "lolcathost") db_port=env.int("PORT", 10101)# export CONNECTION_URL=https://${USER:-sloria}:${PASSWORD}@${HOST:-localhost}/# export PASSWORD=secret# export YEAR=${CURRENT_YEAR:-2020}fromenvironsimportEnvenv=Env(expand_vars=True) connection_url=env("CONNECTION_URL") # =>'https://sloria:secret@localhost'year=env.int("YEAR") # =>2020# export TTL=-2# export NODE_ENV='invalid'# export EMAIL='^_^'fromenvironsimportEnvfrommarshmallow.validateimportOneOf, Length, Emailenv=Env() # simple validatorenv.int("TTL", validate=lambdan: n>0) # => Environment variable "TTL" invalid: ['Invalid value.']# using marshmallow validatorsenv.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 validatorsenv.str("EMAIL", validate=[Length(min=4), Email()]) # => Environment variable "EMAIL" invalid: ['Shorter than minimum length 4.', 'Not a valid email address.']By default, a validation error is raised immediately upon calling a parser method for an invalid environment variable. To defer validation and raise an exception with the combined error messages for all invalid variables, pass eager=False to Env. Call env.seal() after all variables have been parsed.
# export TTL=-2# export NODE_ENV='invalid'# export EMAIL='^_^'fromenvironsimportEnvfrommarshmallow.validateimportOneOf, Email, Length, Rangeenv=Env(eager=False) TTL=env.int("TTL", validate=Range(min=0, max=100)) NODE_ENV=env.str( "NODE_ENV", validate=OneOf( ["production", "development"], error="NODE_ENV must be one of:{choices}" ), ) EMAIL=env.str("EMAIL", validate=[Length(min=4), Email()]) env.seal() # environs.EnvValidationError: Environment variables invalid:{'TTL': ['Must be greater than or equal to 0 and less than or equal to 100.'], 'NODE_ENV': ['NODE_ENV must be one of: production, development'], 'EMAIL': ['Shorter than minimum length 4.', 'Not a valid email address.']}env.seal() validates all parsed variables and prevents further parsing (calling a parser method will raise an error).
# serialize to a dictionary of simple types (numbers and strings)env.dump() #{'COORDINATES': [23.3, 50.0],# 'ENABLE_FEATURE_X': False,# 'ENABLE_LOGIN': True,# 'GITHUB_REPOS': ['webargs', 'konch', 'ped'],# 'GITHUB_USER': 'sloria',# 'MAX_CONNECTIONS': 100,# 'MYAPP_HOST': 'lolcathost',# 'MYAPP_PORT': 3000,# 'SHIP_DATE': '1984-06-25',# 'TTL': 42}# export DOMAIN='http://myapp.com'# export COLOR=invalidfromfurlimportfurl# Register a new parser method for paths@env.parser_for("furl")deffurl_parser(value): returnfurl(value) domain=env.furl("DOMAIN") # => furl('https://myapp.com')# Custom parsers can take extra keyword arguments@env.parser_for("enum")defenum_parser(value, choices): ifvaluenotinchoices: raiseenvirons.EnvError("Invalid!") returnvaluecolor=env.enum("COLOR", choices=["black"]) # => raises EnvError# myapp/settings.pyfromenvironsimportEnvenv=Env() env.read_env() # Override in .env for local developmentDEBUG=env.bool("FLASK_DEBUG", default=False) # SECRET_KEY is requiredSECRET_KEY=env.str("SECRET_KEY")Load the configuration after you initialize your app.
# myapp/app.pyfromflaskimportFlaskapp=Flask(__name__) app.config.from_object("myapp.settings")For local development, use a .env file to override the default configuration.
# .env DEBUG=true SECRET_KEY="not so secret"Note: Because environs depends on python-dotenv, the flask CLI will automatically read .env and .flaskenv files.
environs includes a number of helpers for parsing connection URLs. To install environs with django support:
pip install environs[django] Use env.dj_db_url, env.dj_cache_url and env.dj_email_url to parse the DATABASE_URL, CACHE_URL and EMAIL_URL environment variables, respectively.
For more details on URL patterns, see the following projects that environs is using for converting URLs.
Basic example:
# myproject/settings.pyfromenvironsimportEnvenv=Env() env.read_env() # Override in .env for local developmentDEBUG=env.bool("DEBUG", default=False) # SECRET_KEY is requiredSECRET_KEY=env.str("SECRET_KEY") # Parse database URLs, e.g. "postgres://localhost:5432/mydb"DATABASES={"default": env.dj_db_url("DATABASE_URL")} # Parse email URLs, e.g. "smtp://"email=env.dj_email_url("EMAIL_URL", default="smtp://") EMAIL_HOST=email["EMAIL_HOST"] EMAIL_PORT=email["EMAIL_PORT"] EMAIL_HOST_PASSWORD=email["EMAIL_HOST_PASSWORD"] EMAIL_HOST_USER=email["EMAIL_HOST_USER"] EMAIL_USE_TLS=email["EMAIL_USE_TLS"] # Parse cache URLS, e.g "redis://localhost:6379/0"CACHES={"default": env.dj_cache_url("CACHE_URL")}For local development, use a .env file to override the default configuration.
# .env DEBUG=true SECRET_KEY="not so secret"For a more complete example, see django_example.py in the examples/ directory.
See The 12-factor App section on configuration.
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 expanded variables
- serialize your configuration to JSON, YAML, etc.
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:
- Make it easy to extend parsing behavior and develop plugins.
- Leverage the deserialization and validation functionality provided by a separate library (marshmallow).
- Clean up redundant API.
See this GitHub issue which details specific differences with envparse.
MIT licensed. See the LICENSE file for more details.