re.py 文件源码

def _compile(*key):
    # internal: compile pattern
    pattern, flags = key
    bypass_cache = flags & DEBUG
    if not bypass_cache:
        cachekey = (type(key[0]),) + key
        try:
            p, loc = _cache[cachekey]
            if loc is None or loc == _locale.setlocale(_locale.LC_CTYPE):
                return p
        except KeyError:
            pass
    if isinstance(pattern, _pattern_type):
        if flags:
            raise ValueError('Cannot process flags argument with a compiled pattern')
        return pattern
    if not sre_compile.isstring(pattern):
        raise TypeError, "first argument must be string or compiled pattern"
    try:
        p = sre_compile.compile(pattern, flags)
    except error, v:
        raise error, v # invalid expression
    if not bypass_cache:
        if len(_cache) >= _MAXCACHE:
            _cache.clear()
        if p.flags & LOCALE:
            if not _locale:
                return p
            loc = _locale.setlocale(_locale.LC_CTYPE)
        else:
            loc = None
        _cache[cachekey] = p, loc
    return p