<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_vexrc(options, environ):
 """Get a representation of the contents of the config file. :returns: a Vexrc instance. """

    # Complain if user specified nonexistent file with --config.
    # But we don't want to complain just because ~/.vexrc doesn't exist.
    if options.config and not os.path.exists(options.config):
        raise exceptions.InvalidVexrc("nonexistent config: {0!r}".format(options.config))
    filename = options.config or os.path.expanduser('~/.vexrc')
    vexrc = config.Vexrc.from_file(filename, environ)
    return vexrc