Set configuration files with Jinja2

config.py

#!/usr/bin/env python

import os
import sys
from jinja2 import Environment, FileSystemLoader

def set_environment(template_dir):
  env = Environment(loader=FileSystemLoader(template_dir), trim_blocks=True)
  env.globals['env_var'] = lambda varname, default='': os.getenv(varname, default)
  env.globals['exists'] = lambda varname: varname in os.environ
  return env

def replace_variables():
  template_file = os.path.abspath(sys.argv[1])
  template_dir = os.path.dirname(template_file)
  env = set_environment(template_dir)
  print env.get_template(os.path.basename(template_file)).render()

if __name__ == '__main__':
  replace_variables()