Usage

In order to use Yapconf in a project, you will first need to create your specification object. There are lots of options for this object, so we’ll just start with the basics. Check out the Item Arguments section for all the options available to you. For now, let’s just assume we have the following specification defined

from yapconf import YapconfSpec

my_spec = YapconfSpec({
    'db_name': {'type': 'str'},
    'db_port': {'type': 'int'},
    'db_host': {'type': 'str'},
    'verbose': {'type': 'bool', 'default': True},
    'filename': {'type': 'str'},
})

Now that you have a specification for your configuration, you can load your config from lots of different places using load_config. When using this method, it is significant the order in which you pass your arguments as it sets the precedence for load order. Let’s see this in practice:

# Let's say you loaded this dict from the command-line (more on that later)
cli_args = {'filename': '/path/to/config', 'db_name': 'db_from_cli'}

# Also assume you have /some/config.yml that has the following:
#   db_name: db_from_config_file
#   db_port: 1234
config_file = '/some/config.yml' # JSON is also supported!

# Finally, let's assume you have the following set in your environment
# DB_NAME="db_from_environment"
# FILENAME="/some/default/config.yml"
# DB_HOST="localhost"

# You can load your config:
config = my_spec.load_config(cli_args, config_file, 'ENVIRONMENT')


# You now have a config object which can be accessed via attributes or keys:
config.db_name # > db_from_cli
config['db_port'] # > 1234
config.db_host # > localhost
config['verbose'] # > True
config.filename # > /path/to/config

# If you loaded in a different order, you'll get a different result
config = my_spec.load_config('ENVIRONMENT', config_file, cli_args)
config.db_name # > db_from_environment

This config object is powered by python-box which is a handy utility for handling your config object. It behaves just like a dictionary and you can treat it as such!

Nested Items

In a lot of cases, it makes sense to nest your configuration, for example, if we wanted to take all of our database configuration and put it into a single dictionary, that would make a lot of sense. You would specify this to yapconf as follows:

nested_spec = YapconfSpec({
    'db': {
        'type': 'dict',
        'items': {
            'name': { 'type': 'str' },
            'port': { 'type': 'int' }
        }
    }
})

config = nested_spec.load_config({'db': {'name': 'db_name', 'port': 1234}})

config.db.name # returns 'name'
config.db.port # returns 1234
config.db # returns the db dictionary

List Items

List items are a special class of nested items which is only allowed to have a single item listed. It can be specified as follows:

list_spec = YapconfSpec({
    'names': {
        'type': 'list',
        'items': {
            'name': {'type': 'str'}
        }
    }
})

config = list_spec.load_config({'names': ['a', 'b', 'c']})

config.names # returns ['a', 'b', 'c']

Environment Loading

If no env_name is specified for each item, then by default, Yapconf will automatically format the item’s name to be all upper-case and snake case. So the name foo_bar will become FOO_BAR and fooBar will become FOO_BAR. If you do not want to apply this formatting, set format_env to False. Loading list items and dict items from the environment is not supported and as such env_name s that are set for these items will be ignored.

Often times, you will want to prefix environment variables with your application name or something else. You can set an environment prefix on the YapconfSpec item via the env_prefix:

import os

env_spec = Specification({'foo': {'type': 'str'}}, 'MY_APP_')

os.environ['FOO'] = 'not_namespaced'
os.environ['MY_APP_FOO'] = 'namespaced_value'

config = env_spec.load_config('ENVIRONMENT')

config.foo # returns 'namespaced_value'

Note

When using an env_name with env_prefix the env_prefix will still be applied to the name you provided. If you want to avoid this behavior, set the apply_env_prefix to False.

As of version 0.1.2, you can specify additional environment names via: alt_env_names. The apply_env_prefix flag will also apply to each of these. If your environment names collide with other names, then an error will get raised when the specification is created.

CLI Support

Yapconf has some great support for adding your configuration items as command-line arguments by utilizing argparse. Let’s assume the my_spec object from the original example

import argparse

my_spec = YapconfSpec({
    'db_name': {'type': 'str'},
    'db_port': {'type': 'int'},
    'db_host': {'type': 'str'},
    'verbose': {'type': 'bool', 'default': True},
    'filename': {'type': 'str'},
})

parser = argparser.ArgumentParser()
my_spec.add_arguments(parser)

args = [
    '--db-name', 'db_name',
    '--db-port', '1234',
    '--db-host', 'localhost',
    '--no-verbose',
    '--filename', '/path/to/file'
]

cli_values = vars(parser.parse_args(args))

config = my_spec.load_config(cli_values)

config.db_name # 'db_name'
config.db_port # 1234
config.db_host # 'localhost'
config.verbose # False
config.filename # '/path/to/file'

Yapconf makes adding CLI arguments very easy! If you don’t want to expose something over the command line you can set the cli_expose flag to False.

Boolean Items and the CLI

Boolean items will add special flags to the command-line based on their defaults. If you have a default set to True then a --no-{item_name} flag will get added. If the default is False then a --{{item_name}} will get added as an argument. If no default is specified, then both will be added as mutually exclusive arguments.

Nested Items and the CLI

Yapconf even supports list and dict type items from the command-line:

import argparse

spec = YapconfSpec({
    'names': {
        'type': 'list',
        'items': {
            'name': {'type': 'str'}
        }
    },
    'db': {
        'type': 'dict',
        'items': {
            'host': {'type': 'str'},
            'port': {'type': 'int'}
        },
    }
})

parser = argparse.ArgumentParser()

cli_args = [
    '--name', 'foo',
    '--name', 'bar',
    '--db-host', 'localhost',
    '--db-port', '1234',
    '--name', 'baz'
]

cli_values = vars(parser.parse_args(args))

config = my_spec.load_config(cli_values)

config.names # ['foo', 'bar', 'baz']
config.db.host # 'localhost'
config.db.port # 1234

Limitations

There are a few limitations to how far down the rabbit-hole Yapconf is willing to go. Yapconf does not support list type items with either dict or list children. The reason is that it would be very cumbersome to start specifying which items belong to which dictionaries and in which index in the list.

CLI/Environment Name Formatting

A quick note on formatting and yapconf. Yapconf tries to create sensible ways to convert your config items into “normal” environment variables and command-line arguments. In order to do this, we have to make some assumptions about what “normal” environment variables and command-line arguments are.

By default, environment variables are assumed to be all upper-case, snake-case names. The item name foO_BaR would become FOO_BAR in the environment.

By default, command-line argument are assumed to be kebab-case. The item name foo_bar would become --foo-bar

If you do not like this formatting, then you can turn it off by setting the format_env and format_cli flags.

Config Migration

Throughout the lifetime of an application it is common to want to move configuration around, changing both the names of configuration items and the default values for each. Yapconf also makes this migration a breeze! Each item has a previous_defaults and previous_names values that can be specified. These values help you migrate previous versions of config files to newer versions. Let’s see a basic example where we might want to update a config file with a new default:

# Assume we have a JSON config file ('/path/to/config.json') like the following:
# {"db_name": "test_db_name", "db_host": "1.2.3.4"}

spec = YapconfSpec({
    'db_name': {'type': 'str', 'default': 'new_default', 'previous_defaults': ['test_db_name']},
    'db_host': {'type': 'str', 'previous_defaults': ['localhost']}
})

# We can migrate that file quite easily with the spec object:
spec.migrate_config_file('/path/to/config.json')

# Will result in /path/to/config.json being overwritten:
# {"db_name": "new_default", "db_host": "1.2.3.4"}

You can specify different output config files also:

spec.migrate_config_file('/path/to/config.json',
                         output_file_name='/new/path/to/config.json')

There are many values you can pass to migrate_config_file, by default it looks like this:

spec.migrate_config_file('/path/to/config',
                         always_update=False,    # Always update values (even if you set them to None)
                         current_file_type=None, # Used for transitioning between json and yaml config files
                         output_file_name=None,  # Will default to current file name
                         output_file_type=None,  # Used for transitioning between json and yaml config files
                         create=True,            # Create the file if it doesn't exist
                         update_defaults=True    # Update the defaults
                         )

YAML Support

Yapconf knows how to output and read both json and yaml files. However, to keep the dependencies to a minimum it does not come with yaml. You will have to manually install either pyyaml or ruamel.yaml if you want to use yaml.

Item Arguments

For each item in a specification, you can set any of these keys:

Name	Default	Description
name	N/A	The name of the config item
item_type	'str'	The python type of the item ('str', 'int', 'long', 'float', 'bool', 'complex', 'dict', 'list' )
default	None	The default value for this item
env_name	name.upper()	The name to search in the environment
description	None	Description of the item
required	True	Specifies if the item is required to exist
cli_short_name	None	One-character command-line shortcut
cli_choices	None	List of possible values for the item from the command-line
previous_names	None	List of previous names an item had
previous_defaults	None	List of previous defaults an item had
items	None	Nested item definition for use by list or dict type items
cli_expose	True	Specifies if this item should be added to arguments on the command-line (nested list are always False)
separator	.	The separator to use for dict type items (useful for previous_names)
bootstrap	False	A flag that indicates this item needs to be loaded before others can be loaded
format_env	True	A flag to determine if environment variables will be all upper-case SNAKE_CASE.
format_cli	True	A flag to determine if we should format the command-line arguments to be kebab-case.
apply_env_prefix	True	Apply the env_prefix even if the environment name was set manually. Ignored if format_env is False
choices	None	A list of valid choices for the item. Cannot be set for dict items.
alt_env_names	[]	A list of alternate environment names.