diff options
Diffstat (limited to 'Lib/cmpcache.py')
| -rw-r--r-- | Lib/cmpcache.py | 100 |
1 files changed, 48 insertions, 52 deletions
diff --git a/Lib/cmpcache.py b/Lib/cmpcache.py index 5446e66..93332b7 100644 --- a/Lib/cmpcache.py +++ b/Lib/cmpcache.py @@ -1,13 +1,12 @@ -# 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 +"""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 * @@ -19,50 +18,47 @@ import statcache 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, shallow=1): - # 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 + """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 -# 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] + """Return signature (i.e., type, size, mtime) from raw stat data.""" + 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, '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 + """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 |