Eric Fried bab1556735 Add a Quick Start tutorial

As a user completely new to oslo_config (well, I had only experienced it
in the already-implemented context of the nova project), I would like to
have had a reference document that provided a step-by-step guide to
writing a simple test script I could use to noodle around.  It might
have gone something like this.

Change-Id: I02ff56f47ac8b93e0ee37eb55b53552059e4da27

2019-05-03 16:11:49 -06:00

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oslo.config Quick Start!

Are you brand new to oslo.config? This brief tutorial will get you started understanding some of the fundamentals.

Prerequisites

A plain text editor or Python-enabled IDE
A Python interpreter
A command shell from which the interpreter can be invoked
The oslo_config library in your Python path.

Test Script

Put this in a file called oslocfgtest.py.

# The sys module lets you get at the command line arguments.
import sys

# Load up the cfg module, which contains all the classes and methods
# you'll need.
from oslo_config import cfg

# Define an option group
grp = cfg.OptGroup('mygroup')

# Define a couple of options
opts = [cfg.StrOpt('option1'),
        cfg.IntOpt('option2', default=42)]

# Register your config group
cfg.CONF.register_group(grp)

# Register your options within the config group
cfg.CONF.register_opts(opts, group=grp)

# Process command line arguments.  The arguments tell CONF where to
# find your config file, which it loads and parses to populate itself.
cfg.CONF(sys.argv[1:])

# Now you can access the values from the config file as
# CONF.<group>.<opt>
print("The value of option1 is %s" % cfg.CONF.mygroup.option1)
print("The value of option2 is %d" % cfg.CONF.mygroup.option2)

Conf File

Put this in a file called oslocfgtest.conf in the same directory as oslocfgtest.py.

[mygroup]
option1 = foo
# Comment out option2 to test the default value
# option2 = 123

Run It!

From your command shell, in the same directory as your script and conf, invoke:

python oslocfgtest.py --config-file oslocfgtest.conf

Revel in the output being exactly as expected. If you've done everything right, you should see:

The value of option1 is foo
The value of option2 is 42

Now go play with some more advanced option settings!

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