def filter_sections(sections):
    """Filter through pairs (name, options)
    leaving only those that match runtime.

    If no requirements sections found, return None.
    If some sections found, but none matches current runtime, return empty list.
    """
    if not sections:
        return None
    jobs = []
    matchers = python_version_matchers()
    for name, options in sections:
        target_version = options.pop('python', None)
        if target_version in matchers:
            jobs.append((name, options))
    return jobs