RFC: Add a way to disable envvar loading and default prefix

[rochacbruno]

It's a great library and I am enjoying it. However I would like to make a small feature request if it is not already there. I want a way to disable environmental variable overwriting the variables declared in config files.
I removed the below line from the Dynaconf() class parameter , still it's the same.
envvar_prefix = "DYNACONF"

I ever created a new "envvarprefix" however , it seems the env prefix "DYNACONF.." is a default and always being checked even if you have a different envvar_prefix set.

Could you please consider below as the feature requests if there is no answer: 1) Is there a way to completely disable the environmental variable overwriting the existing ? 2) Is there a way to completely disable the check up of environmental variable "DYNACONF_" when different envvar_prefix is like below ? envvar_prefix = "MYAPP"

Originally posted by @swagatsourav in https://github.com/dynaconf/dynaconf/discussions/781

[b4stien]

I removed the below line from the Dynaconf() class parameter , still it's the same. envvar_prefix = "DYNACONF"

The doc says DYNACONF it's the default value for envvar_prefix anyway (cf this paragraph), as expected, removing the explicit set to the default has no effect.

Your 2. sounds like a bug.

For 1., deep down inside the paragraph for external loader there is a hint towards LOADERS_FOR_DYNACONF to do what you want. If you pass an empty list you might be able to disable the default environment variable lookup.

(Take all this with a grain of salt, I've just read the doc and never used the software)

[swagatsourav]

I removed the below line from the Dynaconf() class parameter , still it's the same. envvar_prefix = "DYNACONF"

The doc says DYNACONF it's the default value for envvar_prefix anyway (cf this paragraph), as expected, removing the explicit set to the default has no effect.

Your 2. sounds like a bug.

For 1., deep down inside the paragraph for external loader there is a hint towards LOADERS_FOR_DYNACONF to do what you want. If you pass an empty list you might be able to disable the default environment variable lookup.

(Take all this with a grain of salt, I've just read the doc and never used the software)

@b4stien , Thanks for the suggestion on point no 1. It's working.

[pedro-psb]

2. Is there a way to completely disable the check up of environmental variable "DYNACONF_" when different envvar_prefix is like below?

There is also a workaround. This example from the docs achieves that with filtering strategies.

from dynaconf import Dynaconf
from dynaconf.strategies.filtering import PrefixFilter

settings = Dynaconf(
    settings_file="settings.toml",
    environments=False,
    filter_strategy=PrefixFilter("prefix")
)

After that, env var that have a different prefix than that specified in the PrefixFilter won't get loaded.

Still, I think this should be the default too.

[techdragon]

I think solving this could also be a way to solve an issue I've had occasionally.

It would be good to be able to filter the loading process so that only a specific set of desired variables are parsed in, without the need to create a settings file, or modify them with a prefix... A way to say "only these variables please" from a code + environment variables pathway where there's no additional files getting created. While I could go around injecting settings files into my Kubernetes pods, I prefer to simply use environment variables wherever possible and in the case of library code that might get reused, having as narrow a scope as possible is a good thing.

If there was a way to filter the loaded environment variables it would enable the ability to set that filter to an "empty list" and thus disable loading anything via the environment variables.

[rochacbruno]

@techdragon you can pass https://www.dynaconf.com/envvars/#environment-variables-filtering ignore_unknown_envvars=True and then it will load only variables that are defined.

You can define a variable via Validators or to the instance initialization

app.py

settings = Dynaconf(
    ignore_unknown_envvars=True,
    thing="default value",
    envvar_prefix=False
)

export THING="other value"
export IGNORED=0
dynaconf -i app.settings list

THING<str>:"other value"

[mitches-got-glitches]

I've just come across this too thinking it seemed like a bug, certainly unexpected.

Reproduced this with Python 3.11.4 and dynaconf 3.2.4:

import os

from dynaconf import Dynaconf
from dynaconf.strategies.filtering import PrefixFilter

os.environ["APP_CLASSIFIER"] = "logistic_regression"
os.environ["DYNACONF_DEBUG"] = "true"
os.environ["DYNACONF_BLADE"] = "runner"
# This will take precedence over DYNACONF_DEBUG if uncommented.
# os.environ["APP_DEBUG"] = "false"

settings = Dynaconf(envvar_prefix="APP")
# Adding the filter too only returns those prefixed with "APP_".
# But seems like unnecessary repetition - should be the default?
# settings = Dynaconf(envvar_prefix="APP", filter_strategy=PrefixFilter("APP"))

if __name__ == "__main__":
    print(settings.classifier)
    >>> "logistic_regression"
    # These shouldn't be available...
    print(settings.debug)
    >>> True
    # If APP_DEBUG uncommented:
    # >>> False
    print(settings.blade)
    >>> "runner"

I think I would upvote making it the default to exclude any env vars prefixed with "DYNACONF" when another prefix is specified to avoid polluting the settings space unintentionally.

[rochacbruno]

1156 to take care of it