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Declare and load configuration from environment variables

Project description

Declare and load configuration from environment variables.

Supported features:

  • declare different sets of variables for production, test and other environments

  • load variables from file if necessary

  • parse configuration into different datatypes

    • str
    • int
    • float
    • bool (‘True’, ‘False’, 1, 0, ‘yes’, ‘no’)
    • str[]
    • int[]
    • float[]
    • bool[]
    • nested types
  • easy to work with reports about missing variables and declaration issues

    Missing environment variables:
    export ERR_KEY_1=[your value here]
    export ERR_KEY_1_DICT2_DICT3_KEY4=[your value here]
    export ERR_KEY_1_DICT2_KEY3=[your value here]
    
    Missing declarations:
    declare("undeclared", [your definition here])
    
    Parse errors:
    ERR_KEY_1_VALUE1: invalid literal for int() with base 10: 'some int value'
    

Install

pip install config

Examples

Create a new Config instance

from env_config import

# control error reporting.
# If deferred, config errors are raised the first time Config.get() is called.
# The error message contains a detailed report about all errors encountered while parsing config variables.
# If not deferred, Config raises on the first error encountered. This most likely happens while calling Config.declare().
# Default is defer_raise=True
cfg = Config(defer_raise=False)

# load config from a file. See a more detailed example further down.
cfg = Config(filename_variable='CONFIG_FILE')

Configure log levels

env_config has a simple mechanism to set log levels for python logging, including all configured loggers. The library searches for environment variables that are build following this schema: LOG_LEVEL_{logger_name.upper} If found the values of each variable is applied as the log_level for the respective logger. The environment variable LOG_LEVEL (without a logger name) set the log level for the root logger.

the available values are: - debug - info - warning - error - critical

import os
from env_config import

os.environ['LOG_LEVEL'] = 'info'  # set the root logger to logging.INFO
os.environ['LOG_LEVEL_URLLIB3'] = 'critical'  # set the urllib3 logger to logging.CRITICAL
os.environ['LOG_LEVEL_PARAMIKO.TRANSPORT'] = 'debug'  # set paramiko.transport to logging.DEBUG

cfg = Config()
cfg.apply_log_levels()  # read the environment variables and apply to the respective log levels

Declare and load scalar values

from env_config import Config, parse_int, parse_float, parse_str, parse_bool

cfg = Config()

# declare variables with the appropriate parser
cfg.declare('my_int_variable', parse_int())
cfg.declare('my_float_variable', parse_float())
cfg.declare('my_str_variable', parse_str())
cfg.declare('my_bool_variable', parse_bool())

# load the values

# will load the value of MY_INT_VARIABLE as an int
int_result = cfg.get('my_int_variable')
# will load the value of MY_FLOAT_VARIABLE as a float
float_result  = cfg.get('my_float_variable')
# will load the value of MY_STR_VARIABLE as a str
str_result = cfg.get('my_str_variable')

Declare and load list values

from env_config import Config, parse_int_list

cfg = Config()

# declare variables with the appropriate parser
cfg.declare('my_int_list_variable', parse_int_list())

# load the values

# will load the value of MY_INT_LIST_VARIABLE as a list of ints.
# By default it assumes the elements to be comma separated
int_list_result = cfg.get('my_int_list_variable')

Declare and load nested values

Most libraries need multiple variables to be correctly configured. Nested values help reduce boilerplate necessary to wire configuration with the library.

from env_config import Config, parse_str
import psycopg2

cfg = Config()
cfg.declare(
    'database',
    {
       'dbname': parse_str(),
       'user': parse_str(),
       'password': parse_str()
    },
)

# this will load values from these environment variables and parse them into a dict:
#  - DATABASE_DBNAME
#  - DATABASE_USER
#  - DATABASE_PASSWORD

psyco_config = cfg.get('database')
# the dict will look like this: {'dbname': 'some value', 'user': 'username', 'password': 'vsjkfl'}
psyco_connection = psycopg2.connect(**psyco_config)

Namespace your variables

from env_config import Config, parse_str
import psycopg2

cfg = Config(namespace='my_prefix')
cfg.declare('database')

# the value will be loaded from the environment variable: MY_PREFIX_DATABASE
value = cfg.get('database')

Add validation

from env_config import Config, parse_str, parse_str_list
from validators import email

# config expects validators to raise an Error on failure.
# Since the validators package returns Failures instead of raising, we create a small adapter.
def email_validator(value):
    result = email(value)
    if isinstance(result, ValidationFailure):
        raise ValueError('"{}" is not a valid email address'.format(value))

cfg = Config()

cfg.declare('valid_email', parse_str(validator=email_validator))
# this also works with lists. The validator function is applied to each value separately
cfg.declare('valid_list_of_emails, parse_str_list(validator=email_validator))

valid_email = cfg.get('valid_email')
valid_list_of_emails = cfg.get('valid_list_of_emails')

Reloading configuration at runtime

from env_config import Config, parse_str, reload

cfg = Config()
cfg.declare('some_value', parse_str())
value = cfg.get('some_value')

# Values are actually loaded during declare().
# Changes to the environment at runtime are not picked up automatically.
# Relaoding has to be triggered explicitly.

cfg.reload()

new_value = cfg.get('some_value')

Declaring optional variables

Sometimes you just want to load a subset of all variables. For example most applications nowadays get executed in a live environment and in a testing environment. Another example is different processes, for example a web endpoint and a background worker, sharing configuration setup.

# config.py

from env_config import Config, parse_str

def declare_config(tag):
   required = ('live', 'test')
   test_optional = ('live',)

   cfg = Config()
   # this variable is available both in live and test
   cfg.declare('some_value', parse_str(), required, tag)
   # this variable is only available in live. In test it won't be loaded and only raises an error when accessed.
   cfg.declare('some_other_value', parse_str(), test_optional, tag)
   return cfg
# live-app.py

from config import declare_config

# the active tag is 'live', so all variables tagged with 'live' are required and raise errors when missing.
cfg = declare_config('live')

# access variables
val = cfg.get('some_value')
# something_test.py

from config import declare_config

# the active tag is 'test', so all variables tagged with 'test' are required and raise errors when missing.
# All other variables become optional and only raise errors when accessed with
cfg.declare_config('test')

# access variables
val = cfg.get('some_value')

# raise an error, because the variable is not available in 'test'
val2 = cfg.get('some_other_value')

Loading variables from a file

Sometimes it’s rather cumbersome to declare all the variables explicitly. For example the PyCharm variable declaration is rather awkward to use.

To elegantly deal with these kinds of situations, it’s possible to load variables declared to a tag from a bash file. So only one variable (the file name) has to be declared. The rest is loaded from that file. The file is not evaluated, though. Only export declarations are extracted and parsed into variables.

define the variable holding the file name

export CONFIG_FILE=test.sh

Create a file test.sh with the variable declarations.

#!/usr/bin/env bash

# comment is ignored

HIDDEN_VARIABLE="value not parsed"
export VISIBLE_VARIABLE_1="this value will be available"

function {
   # if the line does not start with export it's ignored
}

# variables inside strings are not expanded. The value will contain the literal :code:`$OTHER_VARIABLE`.
export VARIABLE_CONTAINING_REFERENCE="$OTHER_VARIABLE"

Then setup the CONFIG_FILE variable to load the file.

from env_config import Config, parse_str

# uses the value of CONFIG_FILE as the file name to load variables from
config = Config(filename_variable='CONFIG_FILE', defer_raise=False)
# visible_variable_1 is declared in test and the current tag is test. variable1 will be loaded from test.sh
config.declare('visible_variable_1', parse_int(), ('test',), 'test'))

# visible_variable_2 is declared in the 'default' tag and not available in the config file.
# visible_variable_2 will be ignored because the current tag is 'test'
config.declare('visible_variable_1', parse_int(), ('default',), 'test')

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