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//usr/lib/python2.4/lib-old/cmpcache.py
"""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