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Dynaconf allows the validation of settings parameters, in some cases you may want to validate the settings before starting the program.

Lets say you have settings.toml

version = "1.0.0"
age = 35
name = "Bruno"
DEV_SERVERS = ['', 'localhost', '']
PORT = 8001

PROJECT = "This is not hello_world"

Validating in Python programmatically

At any point of your program you can do:

from dynaconf import Dynaconf, Validator

settings = Dynaconf(
        # Ensure some parameters exists (are required)
        Validator('VERSION', 'AGE', 'NAME', must_exist=True),

        # Ensure some password cannot exist
        Validator('PASSWORD', must_exist=False),

        # Ensure some parameter mets a condition
        # conditions: (eq, ne, lt, gt, lte, gte, identity, is_type_of, is_in, is_not_in)
        Validator('AGE', lte=30, gte=10),

        # validate a value is eq in specific env
        Validator('PROJECT', eq='hello_world', env='production'),

        # Ensure some parameter (string) meets a condition
        # conditions: (len_eq, len_ne, len_min, len_max, cont)
        # Determines the minimum and maximum length for the value
        Validator("NAME", len_min=3, len_max=125),

        # Signifies the presence of the value in a set, text or word
        Validator("DEV_SERVERS", cont='localhost'),

        # Checks whether the length is the same as defined.
        Validator("PORT", len_eq=4),

The above will raise dynaconf.validators.ValidationError("AGE must be lte=30 but it is 35 in env DEVELOPMENT") and dynaconf.validators.ValidationError("PROJECT must be eq='hello_world' but it is 'This is not hello_world' in env PRODUCTION")

Providing default or computed values

Validators can be used to provide default or computed values.

Default values

Validator("FOO", default="A default value for foo")

Then if not able to load the values from files or environment this default value will be set for that key.

Computed values

Sometimes you need some values to be computed by calling functions, just pass a callable to the default argument.

Validator("FOO", default=my_function)


def my_function(settings, validator):
    return "this is computed during validation time"

If you want to be lazy evaluated

from dynaconf.utils.parse_conf import empty, Lazy

Validator("FOO", default=Lazy(empty, formatter=my_function))

You can also use dot-delimited paths for registering validators on nested structures:

# Register validators

    # Ensure the field exists.
    Validator('DATABASE.HOST', must_exist=True),

    # Make the database.password field optional. This is a default behavior.
    Validator('DATABASE.PASSWORD', must_exist=None),

# Fire the validator

Combining validators

Validators can be combined using:

| or operator.

Validator('DATABASE.USER', must_exist=True) | Validator('DATABASE.KEY', must_exist=True)

& and operator.

Validator('DATABASE.HOST', must_exist=True) & Validator('DATABASE.CONN', must_exist=True)

CLI and dynaconf_validators.toml

NEW in 1.0.1

Starting on version 1.0.1 it is possible to define validators in TOML file called dynaconf_validators.toml placed in the same folder as your settings files.

dynaconf_validators.toml equivalent to program above


version = {must_exist=true}
name = {must_exist=true}
password = {must_exist=false}

# dot notation is also supported
'a_big_dict.nested_1.nested_2.nested_3.nested_4' = {must_exist=true, eq=1}

  must_exist = true
  lte = 30
  gte = 10

project = {eq="hello_world"}

Then to fire the validation use:

$ dynaconf validate

This returns code 0 (success) if validation is ok.