text: import os
  
  from charmhelpers.core import host
  from charmhelpers.core import hookenv
  
  
  def render(source, target, context, owner='root', group='root',
             perms=0o444, templates_dir=None):
      """
      Render a template.
  
      The `source` path, if not absolute, is relative to the `templates_dir`.
  
      The `target` path should be absolute.
  
      The context should be a dict containing the values to be replaced in the
      template.
  
      The `owner`, `group`, and `perms` options will be passed to `write_file`.
  
      If omitted, `templates_dir` defaults to the `templates` folder in the charm.
  
      Note: Using this requires python-jinja2; if it is not installed, calling
      this will attempt to use charmhelpers.fetch.apt_install to install it.
      """
      try:
          from jinja2 import FileSystemLoader, Environment, exceptions
      except ImportError:
          try:
              from charmhelpers.fetch import apt_install
          except ImportError:
              hookenv.log('Could not import jinja2, and could not import '
                          'charmhelpers.fetch to install it',
                          level=hookenv.ERROR)
              raise
          apt_install('python-jinja2', fatal=True)
          from jinja2 import FileSystemLoader, Environment, exceptions
  
      if templates_dir is None:
          templates_dir = os.path.join(hookenv.charm_dir(), 'templates')
      loader = Environment(loader=FileSystemLoader(templates_dir))
      try:
          source = source
          template = loader.get_template(source)
      except exceptions.TemplateNotFound as e:
          hookenv.log('Could not load template %s from %s.' %
                      (source, templates_dir),
                      level=hookenv.ERROR)
          raise e
      content = template.render(context)
      host.mkdir(os.path.dirname(target), owner, group)
      host.write_file(target, content, owner, group, perms)
  