Environment variables

overloading parameters via env vars

All configuration parameters, including custom environments and dynaconf configuration, can be overridden through environment variables.

To override the configuration parameter {param}, use an environment variable named DYNACONF_{PARAM}. For instance, to override the “HOST” configuration parameter, you can run your application with:

DYNACONF_HOST='otherhost.com' python yourapp.py

.env files

If you don’t want to declare the variables on every program call you can run export DYNACONF_{PARAM} in your shell or put the values in a .env file located in the same directory as your settings files (the root directory of your application or the same folder where your program script is located), variables in .env does not overrride existing environment variables.

IMPORTANT: Dynaconf will search for a .env on the order explained here. So to avoid conflicts with existing .env in parent directories it is recommended to have a .env inside your project even if it is empty.

Precedence and type casting

Environment variables take precedence over all other configuration sources: if the variable is set, it will be used as the value for the parameter even if parameter exists in settings files or in .env.

Variable values are parsed as if they were TOML syntax. As illustration, consider the following examples:

# Numbers
DYNACONF_INTEGER=42
DYNACONF_FLOAT=3.14

# Text
DYNACONF_STRING=Hello
DYNACONF_STRING="Hello"

# Booleans
DYNACONF_BOOL=true
DYNACONF_BOOL=false

# Use extra quotes to force a string from other type
DYNACONF_STRING="'42'"
DYNACONF_STRING="'true'"

# Arrays must be homogenous in toml syntax
DYNACONF_ARRAY=[1, 2, 3]
DYNACONF_ARRAY=[1.1, 2.2, 3.3]
DYNACONF_ARRAY=['a', 'b', 'c']

# Dictionaries
DYNACONF_DICT={key="abc",val=123}
# toml syntax does not allow `None/null` values so use @none
DYNACONF_NONE='@none None'

# toml syntax does not allow mixed type arrays so use @json
DYNACONF_ARRAY='@json [42, 3.14, "hello", true, ["otherarray"], {"foo": "bar"}]'
NOTE: Older versions of Dynaconf used the @casting prefixes for env vars like export DYNACONF_INTEGER='@int 123' still works but this casting is deprecated in favor of using TOML syntax described above. To disable the @casting do export AUTO_CAST_FOR_DYNACONF=false

Merging new data to existing variables

Nested keys in dictionaries via environment variables.

New in 2.1.0

This is useful for Django settings.

Lets say you have a configuration like this:

settings.py

DATABASES = {
    'default': {
        'NAME': 'db',
        'ENGINE': 'module.foo.engine',
        'ARGS': {'timeout': 30}
    }
}

And now you want to change the values of ENGINE to other.module, via environment variables you can use the format ${ENVVAR_PREFIX}_${VARIABLE}__${NESTED_ITEM}__${NESTED_ITEM}

Each __ (dunder, a.k.a double underline) denotes access to nested elements in a dictionary.

So

DATABASES['default']['ENGINE'] = 'other.module'

Can be expressed as environment variables as:

export DYNACONF_DATABASES__default__ENGINE=other.module
NOTE: if you are using Django extension then the prefix will be DJANGO_ instead of DYNACONF_ and the same if you are using FLASK_ or a custom prefix if you have customized the ENVVAR_PREFIX.

This will result in

DATABASES = {
    'default': {
        'NAME': 'db',
        'ENGINE': 'other.module',
        'ARGS': {'timeout': 30}
    }
}
IMPORTANT lower case keys are respected only on *nix systems, unfortunately Windows environment variables are case insensitive and Python reads it as all upper cases, that means that if you are running on Windows the dictionary can have only upper case keys.

Now if you want to add a new item to ARGS key:

export DYNACONF_DATABASES__default__ARGS__retries=10

This will result in

DATABASES = {
    'default': {
        'NAME': 'db',
        'ENGINE': 'other.module',
        'ARGS': {'timeout': 30, 'retries': 10}
    }
}

and you can also pass a toml like dictionary to be merged with existing ARGS key.

export DYNACONF_DATABASES__default__ARGS='{timeout=50, size=1}'

will result in

DATABASES = {
    'default': {
        'NAME': 'db',
        'ENGINE': 'other.module',
        'ARGS': {'retries': 10, 'timeout': 50, 'size': 1}
    }
}

Now if you want to clean an existing nested attribute you can use the @reset token on exported env var.

export DYNACONF_DATABASES__default__ARGS='@reset {}'

This will result in

DATABASES = {
    'default': {
        'NAME': 'db',
        'ENGINE': 'other.module',
        'ARGS': {}
    }
}

And also you can do a @reset followed by a re-assignment

Dynaconf env vars are parsed using toml so the format for dictionaries is a bit different.
export DYNACONF_DATABASES__default__ARGS='@reset {timeout=90}'

This will result in

DATABASES = {
    'default': {
        'NAME': 'db',
        'ENGINE': 'other.module',
        'ARGS': {'timeout': 90}
    }
}

And if in any case you need to completely remove that key from the dictionary:

export DYNACONF_DATABASES__default__ARGS='@del'

This will result in

DATABASES = {
    'default': {
        'NAME': 'db',
        'ENGINE': 'other.module'
    }
}

Using the dynaconf_merge mark on configuration files.

New in 2.0.0

To merge exported variables there is the dynaconf_merge tokens, example:

Your main settings file (e.g settings.toml) has an existing DATABASE dict setting on [default] env.

Now you want to contribute to the same DATABASE key by adding new keys, so you can use dynaconf_merge at the end of your dict:

In specific [envs]

[default]
database = {host="server.com", user="default"}

[development]
database = {user="dev_user", dynaconf_merge=true}

or

New in 2.2.0
[default]
database = {host="server.com", user="default"}

[development.database]
dynaconf_merge = {user="dev_user"}

In an environment variable use @merge token:

New in 2.2.0
# Toml formatted envvar
export DYNACONF_DATABASE='@merge {password=1234}'

or dunder (recommended)

# Toml formatted envvar
export DYNACONF_DATABASE__PASSWORD=1234

The end result will be on [development] env:

settings.DATABASE == {'host': 'server.com', 'user': 'dev_user', 'password': 1234}

Read more in Getting Started Guide

The global prefix

The DYNACONF_{param} prefix is set by ENVVAR_PREFIX_FOR_DYNACONF and serves only to be used in environment variables to override config values.

This prefix itself can be changed to something more significant for your application, however we recommend keeping DYNACONF_{param} as your global env prefix.

Setting ENVVAR_PREFIX_FOR_DYNACONF to false will disable the prefix entirely and cause Dynaconf to load all environment variables. When providing ENVVAR_PREFIX_FOR_DYNACONF as parameter to LazySettings or settings.configure, make sure to give it a Python-native False:

from dynaconf import LazySettings
settings = LazySettings(ENVVAR_PREFIX_FOR_DYNACONF=False)
NOTE: See the Configuring dynaconf section in documentation to learn more on how to use .env variables to configure dynaconf behavior.