Setting options from environment variables when using argparse

Question

I have a script which has certain options that can either be passed on the command line, or from environment variables. The CLI should take precedence if both are present, a

Answer 1

Thought I'd post my solution as the original question/answer gave me a lot of help.

My problem is a little different to Russell's. I'm using OptionParser and instead of an environmental variable for each argument I have just one which simulates the command line.

i.e.

MY_ENVIRONMENT_ARGS = --arg1 "Maltese" --arg2 "Falcon" -r "1930" -h

Solution:

def set_defaults_from_environment(oparser):

    if 'MY_ENVIRONMENT_ARGS' in os.environ:

        environmental_args = os.environ[ 'MY_ENVIRONMENT_ARGS' ].split()

        opts, _ = oparser.parse_args( environmental_args )

        oparser.defaults = opts.__dict__

oparser = optparse.OptionParser()
oparser.add_option('-a', '--arg1', action='store', default="Consider")
oparser.add_option('-b', '--arg2', action='store', default="Phlebas")
oparser.add_option('-r', '--release', action='store', default='1987')
oparser.add_option('-h', '--hardback', action='store_true', default=False)

set_defaults_from_environment(oparser)

options, _ = oparser.parse_args(sys.argv[1:])

Here I don't throw an error if an argument is not found. But if I wish to I could just do something like

for key in options.__dict__:
    if options.__dict__[key] is None:
        # raise error/log problem/print to console/etc