linecache.py 文件源码

def checkcache(filename=None):
    """Discard cache entries that are out of date.
    (This is not checked upon each call!)"""

    if filename is None:
        filenames = cache.keys()
    else:
        if filename in cache:
            filenames = [filename]
        else:
            return

    for filename in filenames:
        size, mtime, lines, fullname = cache[filename]
        if mtime is None:
            continue   # no-op for files loaded via a __loader__
        try:
            stat = os.stat(fullname)
        except os.error:
            del cache[filename]
            continue
        if size != stat.st_size or mtime != stat.st_mtime:
            del cache[filename]