code: def set_environment_var_options(config, env=None, prefix='CONFPY'):
      
      env = env or os.environ
      for section_name, section in config:
  
          for option_name, _ in section:
  
              var_name = '{0}_{1}_{2}'.format(
                  prefix.upper(),
                  section_name.upper(),
                  option_name.upper(),
              )
              env_var = env.get(var_name)
              if env_var:
  
                  setattr(section, option_name, env_var)
  
      return config
docs: Set any configuration options which have an environment var set.
  
      Args:
          config (confpy.core.config.Configuration): A configuration object which
              has been initialized with options.
          env (dict): Optional dictionary which contains environment variables.
              The default is os.environ if no value is given.
          prefix (str): The string prefix prepended to all environment variables.
              This value will be set to upper case. The default is CONFPY.
  
      Returns:
          confpy.core.config.Configuration: A configuration object with
              environment variables set.
  
      The pattern to follow when setting environment variables is:
  
          <PREFIX>_<SECTION>_<OPTION>
  
      Each value should be upper case and separated by underscores.