Simple environment variable parsing
Project description
envparse2 is a simple utility to parse environment variables.
NOTE: envparse2 is a fork of envparse which is no longer maintained, to check original author and code visit <https://github.com/rconradharris/envparse.git>
If you use Heroku and/or subscribe to the tenets of the 12 Factor App you’ll be using a lot of environment variable-based configuration in your app. os.environ is a great choice to start off with but over time you’ll find yourself duplicating quite a bit of code around handling raw environment variables.
envparse2 aims to eliminate this duplicated, often inconsistent parsing code and instead provide a single, easy-to-use wrapper.
Ideas, and code portions, have been taken from django-environ project but made framework agnostic.
Installing
Through PyPI:
$ pip install envparse2
Usage
In your settings or configuration module, first either import the standard parser or one with a schema:
# Standard
from envparse2 import env
# Schema
from envparse2 import Env
env = Env(BOOLEAN_VAR=bool, LIST_VAR=dict(cast=list, subcast=int))
env can then be called in two ways:
Type explicit: env('ENV_VAR_NAME', cast=TYPE, ...)
Type implicit (for Python builtin types only): env.TYPE('ENV_VAR_NAME', ...) If type is not specified, explicitly or implicitly, then the default type is str.
Casting to a specified type:
# Environment variable: MAIL_ENABLED=1
mail_enabled = env('MAIL_ENABLED', cast=bool)
# OR mail_enabled = env.bool('MAIL_ENABLED')
assert mail_enabled is True
Casting nested types:
# Environment variable: FOO=1,2,3
foo = env('FOO'), subcast=int)
# OR: foo = env('FOO', cast=list, subcast=int)
# Note that there is no way to implicitly call subcast.
assert foo == [1, 2, 3]
Specifying defaults:
# Environment variable MAX_ROWS has not been defined
max_rows = env.int('MAX_ROWS', default=100)
assert max_rows == 100
Proxying values, useful in Heroku for wiring up the environment variables they provide to the ones that your app actually uses:
# Environment variables: MAILGUN_SMTP_LOGIN=foo,
# SMTP_LOGIN='{{MAILGUN_SMTP_LOGIN}}'
smtp_login = env('SMTP_LOGIN')
assert smtp_login == 'foo'
Now if you switch to using Mandrill as an email provider, instead of having to modify your app, you can simply make a configuration change:
SMTP_LOGIN='{{MANDRILL_UESRNAME}}'
There are also a few convenience methods:
env.json: parses JSON and returns a dict.
env.url: parses a url and returns a urlparse.ParseResult object.
Type specific notes:
list: the expected environment variable format is FOO=1,2,3 and may contain spaces between the commas as well as preceding or trailing whitespace.
dict: the expected environment variable format is FOO='key1=val1, key2=val2. Spaces are also allowed.
json: a regular JSON string such as FOO='{"foo": "bar"}' is expected.
Schemas
Define a schema so you can only need to provide the cast, subcast, and defaults once:
# Environment variables: MAIL_ENABLED=0, LIST_INT='1,2,3'
# Bind schema to Env object to get schema-based lookups
env = Env(MAIL_ENABLED=bool, SMTP_LOGIN=dict(cast=str, default='foo'),
LIST_INT=dict(cast=list, subcast=int))
assert env('MAIL_ENABLED') is False
assert env('SMTP_LOGIN') == 'foo' # Not defined so uses default
assert env('LIST_INT') == [1, 2, 3]
The Env constructor takes values in the form of either: VAR_NAME=type or VAR_NAME=dict where dict is a dictionary with either one or more of the following keys specified: cast, subcast, default.
Pre- and Postprocessors
Preprocessors are callables that are run on the environment variable string before any type casting takes place:
# Environment variables: FOO=bar
# Preprocessor to change variable to uppercase
to_upper = lambda v: v.upper()
foo = env('FOO', preprocessor=to_upper)
assert foo == 'BAR'
Postprocessors are callables that are run after the type casting takes place. An example of one might be returning a datastructure expected by a framework:
# Environment variable: REDIS_URL='redis://:redispass@127.0.0.1:6379/0'
def django_redis(url):
return {'BACKEND': 'django_redis.cache.RedisCache',
'LOCATION': '{}:{}:{}'.format(url.hostname, url.port, url.path.strip('/')),
'OPTIONS': {'PASSWORD': url.password}}
redis_config = env('REDIS_URL', postprocessor=django_redis)
assert redis_config == {'BACKEND': 'django_redis.cache.RedisCache',
'LOCATION': '127.0.0.1:6379:0', 'OPTIONS': {'PASSWORD': 'redispass'}}
Environment File
Read from a .env file (line delimited KEY=VALUE):
# This recurses up the directory tree until a file called '.env' is found.
env.read_envfile()
# Manually specifying a path
env.read_envfile('/config/.myenv')
# Values can be read as normal
env.int('FOO')
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