Question

I’ve been thinking about ways to automatically setup configuration in my Python applications.

I usually use the following type of approach:

'''config.py'''
class Config(object):
    MAGIC_NUMBER = 44
    DEBUG = True

class Development(Config):
    LOG_LEVEL = 'DEBUG'

class Production(Config):
    DEBUG = False
    REPORT_EMAIL_TO = ["[e-mail]", "[e-mail]"]

Typically, when I’m running the app in different ways I could do something like:

from config import Development, Production

do_something():
    if self.conf.DEBUG:
       pass

def __init__(self, config='Development'):
    if config == "production":
        self.conf = Production
    else:
        self.conf = Development

I like working like this because it makes sense, however I’m wondering if I can somehow integrate this into my git workflow too.

A lot of my applications have separate scripts, or modules that can be run alone, thus there isn’t always a monolithic application to inherit configurations from some root location.

It would be cool if a lot of these scripts and seperate modules could check what branch is currently checked out and make their default configuration decisions based upon that, e.g., by looking for a class in config.py that shares the same name as the name of the currently checked out branch.

Is that possible, and what’s the cleanest way to achieve it?

Is it a good/bad idea?

Answer 1

I’d prefer spinlok‘s method, but yes, you can do pretty much anything you want in your __init__, e.g.:

import inspect, subprocess, sys

def __init__(self, config='via_git'):
    if config == 'via_git':
        gitsays = subprocess.check_output(['git', 'symbolic-ref', 'HEAD'])
        cbranch = gitsays.rstrip('\n').replace('refs/heads/', '', 1)
        # now you know which branch you're on...
        tbranch = cbranch.title() # foo -> Foo, for class name conventions
        classes = dict(inspect.getmembers(sys.modules[__name__], inspect.isclass)
        if tbranch in classes:
            print 'automatically using', tbranch
            self.conf = classes[tbranch]
        else:
            print 'on branch', cbranch, 'so falling back to Production'
            self.conf = Production
    elif config == 'production':
        self.conf = Production
    else:
        self.conf = Development

This is, um, “slightly tested” (python 2.7). Note that check_output will raise an exception if git can’t get a symbolic ref, and this also depends on your working directory. You can of course use other subprocess functions (to provide a different cwd for instance).