| """Efficiently compare files, boolean outcome only (equal / not equal). |
| |
| Tricks (used in this order): |
| - Use the statcache module to avoid statting files more than once |
| - Files with identical type, size & mtime are assumed to be clones |
| - Files with different type or size cannot be identical |
| - We keep a cache of outcomes of earlier comparisons |
| - We don't fork a process to run 'cmp' but read the files ourselves |
| """ |
| |
| import os |
| from stat import * |
| import statcache |
| |
| |
| # The cache. |
| # |
| cache = {} |
| |
| |
| def cmp(f1, f2, shallow=1): |
| """Compare two files, use the cache if possible. |
| May raise os.error if a stat or open of either fails. |
| Return 1 for identical files, 0 for different. |
| Raise exceptions if either file could not be statted, read, etc.""" |
| s1, s2 = sig(statcache.stat(f1)), sig(statcache.stat(f2)) |
| if not S_ISREG(s1[0]) or not S_ISREG(s2[0]): |
| # Either is a not a plain file -- always report as different |
| return 0 |
| if shallow and s1 == s2: |
| # type, size & mtime match -- report same |
| return 1 |
| if s1[:2] != s2[:2]: # Types or sizes differ, don't bother |
| # types or sizes differ -- report different |
| return 0 |
| # same type and size -- look in the cache |
| key = f1 + ' ' + f2 |
| if cache.has_key(key): |
| cs1, cs2, outcome = cache[key] |
| # cache hit |
| if s1 == cs1 and s2 == cs2: |
| # cached signatures match |
| return outcome |
| # stale cached signature(s) |
| # really compare |
| outcome = do_cmp(f1, f2) |
| cache[key] = s1, s2, outcome |
| return outcome |
| |
| def sig(st): |
| """Return signature (i.e., type, size, mtime) from raw stat data.""" |
| return S_IFMT(st[ST_MODE]), st[ST_SIZE], st[ST_MTIME] |
| |
| def do_cmp(f1, f2): |
| """Compare two files, really.""" |
| #print ' cmp', f1, f2 # XXX remove when debugged |
| bufsize = 8*1024 # Could be tuned |
| fp1 = open(f1, 'rb') |
| fp2 = open(f2, 'rb') |
| while 1: |
| b1 = fp1.read(bufsize) |
| b2 = fp2.read(bufsize) |
| if b1 != b2: return 0 |
| if not b1: return 1 |