Feature Request: Add Support for Prefix in Env Constructor

[arthurc0102]

Hi,

I have a use case where all required environment variables need to share a common prefix. To simplify configuration and avoid redundancy, I propose adding a prefix argument to the Env constructor. For example:

from environs import Env

env = Env(prefix='MYAPP_')

# Instead of accessing `env('MYAPP_VAR')`, we could directly access:
value = env('VAR')  # Automatically resolves to 'MYAPP_VAR'

This feature could enhance the usability of environs for projects that follow naming conventions for environment variables.

If this idea aligns with the project's direction, I'd be happy to implement it and submit a pull request.

[sloria]

environs already supports prefixes: https://github.com/sloria/environs?tab=readme-ov-file#handling-prefixes

[arthurc0102]

I know environs already supported, but it requires using the context manager approach. I am using it in Django to read settings, and all my settings start with DJANGO_ prefix. Following the previous implementation, it was not very convenient. Therefore, I proposed allowing users to pass in a prefix at the beginning.

[sloria]

@arthurc0102 why is the context manager less convenient?

[arthurc0102]

The current usage is as follows (part of settings.py):

env = environs.Env()
env.read_env(path=str(BASE_DIR / ".env"), recurse=False)

# Quick-start development settings - unsuitable for production
# See https://docs.djangoproject.com/en/5.1/howto/deployment/checklist/

# SECURITY WARNING: keep the secret key used in production secret!
SECRET_KEY = env.str("SECRET_KEY")

# SECURITY WARNING: don't run with debug turned on in production!
DEBUG = env.bool("DEBUG", default=(MODE == "local"))

ALLOWED_HOSTS = env.list("ALLOWED_HOSTS", default=[])

All environment variables here start with DJANGO_, e.g., DJANGO_SECRET_KEY. In this scenario, we would need to wrap the entire file in a context manager or write multiple with statements.

[sloria]

yeah, I suppose if all your environment variables have the same prefix, the ctor argument is slightly more convenient and avoids having to indent the whole file.

i've implemented this in #387

[arthurc0102]

Thank you for implementing this feature and releasing a new version!