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- # Module 'cmpcache'
- #
- # 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 = {}
-
-
- # Compare two files, use the cache if possible.
- # May raise os.error if a stat or open of either fails.
- #
- def cmp(f1, f2):
- # 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 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
-
- # Return signature (i.e., type, size, mtime) from raw stat data.
- #
- def sig(st):
- return S_IFMT(st[ST_MODE]), st[ST_SIZE], st[ST_MTIME]
-
- # Compare two files, really.
- #
- def do_cmp(f1, f2):
- #print ' cmp', f1, f2 # XXX remove when debugged
- bufsize = 8*1024 # Could be tuned
- fp1 = open(f1, 'r')
- fp2 = open(f2, 'r')
- while 1:
- b1 = fp1.read(bufsize)
- b2 = fp2.read(bufsize)
- if b1 <> b2: return 0
- if not b1: return 1
-