I've been using optparse for a while now, and would like to add the ability to load the arguments from a config file.
So far the best I can think of is a wrapper batch script with the arguments hardcoded... seems clunky.
What is the most elegant way to do this?
That's what the set_defaults function is for. http://docs.python.org/library/optparse.html#optparse.OptionParser.set%5Fdefaults
Create a file that's the dictionary of default values.
{ 'arg1': 'this',
'arg2': 'that'
}
Then read this file, eval it to convert the text to a dictionary, and provide this dictionary as the arguments to set_defaults.
If you're really worried about eval, then use JSON (or YAML) notation for this file. Or you could even make an .INI file out of it and use configparser to get your defaults.
Or you can use a simple list of assignment statements and exec.
Config File.
arg1 = 'this'
arg2 = 'that'
Reading the config file.
defaults= {}
with open('defaults.py','r') as config
exec config in {}, defaults
I agree with S.Lott's idea of using a config file, but I'd recommend using the built-in ConfigParser (configparser in 3.0) module to parse it, rather than a home-brewed solution.
Here's a brief script that illustrates ConfigParser and optparse in action.
import ConfigParser
from optparse import OptionParser
CONFIG_FILENAME = 'defaults.cfg'
def main():
config = ConfigParser.ConfigParser()
config.read(CONFIG_FILENAME)
parser = OptionParser()
parser.add_option("-l",
"--language",
dest="language",
help="The UI language",
default=config.get("Localization", "language"))
parser.add_option("-f",
"--flag",
dest="flag",
help="The country flag",
default=config.get("Localization", "flag"))
print parser.parse_args()
if __name__ == "__main__":
main()
Output:
(<Values at 0x2182c88: {'flag': 'japan.png', 'language': 'Japanese'}>, [])
Run with "parser.py --language=French":
(<Values at 0x2215c60: {'flag': 'japan.png', 'language': 'French'}>, [])
Help is built in.
Run with "parser.py --help":
Usage: parser.py [options]
Options:
-h, --help show this help message and exit
-l LANGUAGE, --language=LANGUAGE
The UI language
-f FLAG, --flag=FLAG The country flag
The config file:
[Localization]
language=Japanese
flag=japan.png
You can use argparse module for that:
>>> open('args.txt', 'w').write('-f\nbar')
>>> parser = argparse.ArgumentParser(fromfile_prefix_chars='@')
>>> parser.add_argument('-f')
>>> parser.parse_args(['-f', 'foo', '@args.txt'])
Namespace(f='bar')
It might be included in stdlib, see pep 389.
I had a similar problem, but also wanted to specific the config file as an argument. Inspired by S. Lott's answer, I came up with the following code.
Example terminal session:
$ python defaultconf.py # use hard-coded defaults False $ python defaultconf.py --verbose # verbose on command line True $ python defaultconf.py --loadconfig blah # load config with 'verbose':True True $ python defaultconf.py --loadconfig blah --quiet # Override configured value False
Code:
#!/usr/bin/env python2.6
import optparse
def getParser(defaults):
"""Create and return an OptionParser instance, with supplied defaults
"""
o = optparse.OptionParser()
o.set_defaults(**defaults)
o.add_option("--verbose", dest = "verbose", action="store_true")
o.add_option("--quiet", dest = "verbose", action="store_false")
o.add_option("--loadconfig", dest = "loadconfig")
return o
def main():
# Hard coded defaults (including non-command-line-argument options)
my_defaults = {'verbose': False, 'config_only_variable': 42}
# Initially parse arguments
opts, args = getParser(my_defaults).parse_args()
if opts.loadconfig is not None:
# Load config from disk, update the defaults dictionary, and reparse
# Could use ConfigParser, simplejson, yaml etc.
config_file_values = {'verbose': True} # the dict loaded from disk
my_defaults.update(config_file_values)
opts, args = getParser(my_defaults).parse_args()
print opts.verbose
if __name__ == '__main__':
main()
A practical implementation can be found on Github: The defaults dictionary, the argument parser and the main function