IntroductionΒΆ

LayeredConfig compiles configuration from files, environment variables, command line arguments, hard-coded default values, or other backends, and makes it available to your code in a simple way.

from layeredconfig import (LayeredConfig, Defaults, INIFile,
                           Environment, Commandline)

# This represents four different way of specifying the value of the
# configuration option "hello":

# 1. hard-coded defaults
defaults = {"hello": "is it me you're looking for?"}

# 2. INI configuration file
with open("myapp.ini", "w") as fp:
    fp.write("""
[DEFAULT]
hello = kitty
""")

# 3. enironment variables
import os
os.environ['MYAPP_HELLO'] = 'goodbye'

# 4.command-line arguments
import sys
sys.argv = ['./myapp.py', '--hello=world']

# Create a config object that gets settings from these four
# sources.
config = LayeredConfig(Defaults(defaults),
                       INIFile("myapp.ini"),
                       Environment(prefix="MYAPP_"),
                       Commandline())

# Prints "Hello world!", i.e the value provided by command-line
# arguments. Latter sources take precedence over earlier sources.
print("Hello %s!" % config.hello)
  • A flexible system makes it possible to specify the sources of configuration information, including which source takes precedence (Precedence). Implementations of common sources are included (Available sources) and an API for writing new ones exists (Implenting custom ConfigSource classes)
  • Configuration can include subsections (ie. config.downloading.refresh, Subsections) and if a subsection does not contain a requested setting, it can optionally be fetched from the main configuration (if config.module.retry is missing, config.retry can be used instead, Cascading).
  • Configuration settings can be changed by your code (i.e. to update a “lastmodified” setting or similar), and changes can be persisted (saved) to the backend of your choice (Modification and persistance)
  • Configuration settings are typed (ie. if a setting should contain a date, it’s made available to your code as a date object, not a str). If settings are fetched from backends that do not themselves provide typed data (ie. environment variables, which by themselves are strings only), a system for type coercion makes it possible to specify how data should be converted (Typing).