Here's a module I hacked together that reads command-line arguments, environment settings, ini files, and keyring values as well. It's also available in a gist.
"""
Configuration Parser
Configurable parser that will parse config files, environment variables,
keyring, and command-line arguments.
Example test.ini file:
[defaults]
gini=10
[app]
xini = 50
Example test.arg file:
--xfarg=30
Example test.py file:
import os
import sys
import config
def main(argv):
'''Test.'''
options = [
config.Option("xpos",
help="positional argument",
nargs='?',
default="all",
env="APP_XPOS"),
config.Option("--xarg",
help="optional argument",
default=1,
type=int,
env="APP_XARG"),
config.Option("--xenv",
help="environment argument",
default=1,
type=int,
env="APP_XENV"),
config.Option("--xfarg",
help="@file argument",
default=1,
type=int,
env="APP_XFARG"),
config.Option("--xini",
help="ini argument",
default=1,
type=int,
ini_section="app",
env="APP_XINI"),
config.Option("--gini",
help="global ini argument",
default=1,
type=int,
env="APP_GINI"),
config.Option("--karg",
help="secret keyring arg",
default=-1,
type=int),
]
ini_file_paths = [
'/etc/default/app.ini',
os.path.join(os.path.dirname(os.path.abspath(__file__)),
'test.ini')
]
# default usage
conf = config.Config(prog='app', options=options,
ini_paths=ini_file_paths)
conf.parse()
print conf
# advanced usage
cli_args = conf.parse_cli(argv=argv)
env = conf.parse_env()
secrets = conf.parse_keyring(namespace="app")
ini = conf.parse_ini(ini_file_paths)
sources = {}
if ini:
for key, value in ini.iteritems():
conf[key] = value
sources[key] = "ini-file"
if secrets:
for key, value in secrets.iteritems():
conf[key] = value
sources[key] = "keyring"
if env:
for key, value in env.iteritems():
conf[key] = value
sources[key] = "environment"
if cli_args:
for key, value in cli_args.iteritems():
conf[key] = value
sources[key] = "command-line"
print '\n'.join(['%s:\t%s' % (k, v) for k, v in sources.items()])
if __name__ == "__main__":
if config.keyring:
config.keyring.set_password("app", "karg", "13")
main(sys.argv)
Example results:
$APP_XENV=10 python test.py api --xarg=2 @test.arg
<Config xpos=api, gini=1, xenv=10, xini=50, karg=13, xarg=2, xfarg=30>
xpos: command-line
xenv: environment
xini: ini-file
karg: keyring
xarg: command-line
xfarg: command-line
"""
import argparse
import ConfigParser
import copy
import os
import sys
try:
import keyring
except ImportError:
keyring = None
class Option(object):
"""Holds a configuration option and the names and locations for it.
Instantiate options using the same arguments as you would for an
add_arguments call in argparse. However, you have two additional kwargs
available:
env: the name of the environment variable to use for this option
ini_section: the ini file section to look this value up from
"""
def __init__(self, *args, **kwargs):
self.args = args or []
self.kwargs = kwargs or {}
def add_argument(self, parser, **override_kwargs):
"""Add an option to a an argparse parser."""
kwargs = {}
if self.kwargs:
kwargs = copy.copy(self.kwargs)
try:
del kwargs['env']
except KeyError:
pass
try:
del kwargs['ini_section']
except KeyError:
pass
kwargs.update(override_kwargs)
parser.add_argument(*self.args, **kwargs)
@property
def type(self):
"""The type of the option.
Should be a callable to parse options.
"""
return self.kwargs.get("type", str)
@property
def name(self):
"""The name of the option as determined from the args."""
for arg in self.args:
if arg.startswith("--"):
return arg[2:].replace("-", "_")
elif arg.startswith("-"):
continue
else:
return arg.replace("-", "_")
@property
def default(self):
"""The default for the option."""
return self.kwargs.get("default")
class Config(object):
"""Parses configuration sources."""
def __init__(self, options=None, ini_paths=None, **parser_kwargs):
"""Initialize with list of options.
:param ini_paths: optional paths to ini files to look up values from
:param parser_kwargs: kwargs used to init argparse parsers.
"""
self._parser_kwargs = parser_kwargs or {}
self._ini_paths = ini_paths or []
self._options = copy.copy(options) or []
self._values = {option.name: option.default
for option in self._options}
self._parser = argparse.ArgumentParser(**parser_kwargs)
self.pass_thru_args = []
@property
def prog(self):
"""Program name."""
return self._parser.prog
def __getitem__(self, key):
return self._values[key]
def __setitem__(self, key, value):
self._values[key] = value
def __delitem__(self, key):
del self._values[key]
def __contains__(self, key):
return key in self._values
def __iter__(self):
return iter(self._values)
def __len__(self):
return len(self._values)
def get(self, key, *args):
"""
Return the value for key if it exists otherwise the default.
"""
return self._values.get(key, *args)
def __getattr__(self, attr):
if attr in self._values:
return self._values[attr]
else:
raise AttributeError("'config' object has no attribute '%s'"
% attr)
def build_parser(self, options, **override_kwargs):
"""."""
kwargs = copy.copy(self._parser_kwargs)
kwargs.update(override_kwargs)
if 'fromfile_prefix_chars' not in kwargs:
kwargs['fromfile_prefix_chars'] = '@'
parser = argparse.ArgumentParser(**kwargs)
if options:
for option in options:
option.add_argument(parser)
return parser
def parse_cli(self, argv=None):
"""Parse command-line arguments into values."""
if not argv:
argv = sys.argv
options = []
for option in self._options:
temp = Option(*option.args, **option.kwargs)
temp.kwargs['default'] = argparse.SUPPRESS
options.append(temp)
parser = self.build_parser(options=options)
parsed, extras = parser.parse_known_args(argv[1:])
if extras:
valid, pass_thru = self.parse_passthru_args(argv[1:])
parsed, extras = parser.parse_known_args(valid)
if extras:
raise AttributeError("Unrecognized arguments: %s" %
' ,'.join(extras))
self.pass_thru_args = pass_thru + extras
return vars(parsed)
def parse_env(self):
results = {}
for option in self._options:
env_var = option.kwargs.get('env')
if env_var and env_var in os.environ:
value = os.environ[env_var]
results[option.name] = option.type(value)
return results
def get_defaults(self):
"""Use argparse to determine and return dict of defaults."""
parser = self.build_parser(options=self._options)
parsed, _ = parser.parse_known_args([])
return vars(parsed)
def parse_ini(self, paths=None):
"""Parse config files and return configuration options.
Expects array of files that are in ini format.
:param paths: list of paths to files to parse (uses ConfigParse logic).
If not supplied, uses the ini_paths value supplied on
initialization.
"""
results = {}
config = ConfigParser.SafeConfigParser()
config.read(paths or self._ini_paths)
for option in self._options:
ini_section = option.kwargs.get('ini_section')
if ini_section:
try:
value = config.get(ini_section, option.name)
results[option.name] = option.type(value)
except ConfigParser.NoSectionError:
pass
return results
def parse_keyring(self, namespace=None):
"""."""
results = {}
if not keyring:
return results
if not namespace:
namespace = self.prog
for option in self._options:
secret = keyring.get_password(namespace, option.name)
if secret:
results[option.name] = option.type(secret)
return results
def parse(self, argv=None):
"""."""
defaults = self.get_defaults()
args = self.parse_cli(argv=argv)
env = self.parse_env()
secrets = self.parse_keyring()
ini = self.parse_ini()
results = defaults
results.update(ini)
results.update(secrets)
results.update(env)
results.update(args)
self._values = results
return self
@staticmethod
def parse_passthru_args(argv):
"""Handles arguments to be passed thru to a subprocess using '--'.
:returns: tuple of two lists; args and pass-thru-args
"""
if '--' in argv:
dashdash = argv.index("--")
if dashdash == 0:
return argv[1:], []
elif dashdash > 0:
return argv[0:dashdash], argv[dashdash + 1:]
return argv, []
def __repr__(self):
return "<Config %s>" % ', '.join([
'%s=%s' % (k, v) for k, v in self._values.iteritems()])
def comma_separated_strings(value):
"""Handles comma-separated arguments passed in command-line."""
return map(str, value.split(","))
def comma_separated_pairs(value):
"""Handles comma-separated key/values passed in command-line."""
pairs = value.split(",")
results = {}
for pair in pairs:
key, pair_value = pair.split('=')
results[key] = pair_value
return results
