diff options
Diffstat (limited to 'Lib/cmp.py')
| -rw-r--r-- | Lib/cmp.py | 108 |
1 files changed, 55 insertions, 53 deletions
diff --git a/Lib/cmp.py b/Lib/cmp.py index f21d3a240e..943d8bdf48 100644 --- a/Lib/cmp.py +++ b/Lib/cmp.py @@ -1,61 +1,63 @@ -# Module 'cmp' +"""Efficiently compare files, boolean outcome only (equal / not equal). -# Efficiently compare files, boolean outcome only (equal / not equal). - -# Tricks (used in this order): -# - 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 +Tricks (used in this order): + - 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 cache = {} -def cmp(f1, f2, shallow=1): # Compare two files, use the cache if possible. - # Return 1 for identical files, 0 for different. - # Raise exceptions if either file could not be statted, read, etc. - s1, s2 = sig(os.stat(f1)), sig(os.stat(f2)) - if s1[0] <> 8 or s2[0] <> 8: - # 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) - try: - cs1, cs2, outcome = cache[key] - # cache hit - if s1 == cs1 and s2 == cs2: - # cached signatures match - return outcome - # stale cached signature(s) - except KeyError: - # cache miss - pass - # really compare - outcome = do_cmp(f1, f2) - cache[key] = s1, s2, outcome - return outcome +def cmp(f1, f2, shallow=1): + """Compare two files, use the cache if possible. + Return 1 for identical files, 0 for different. + Raise exceptions if either file could not be statted, read, etc.""" + s1, s2 = sig(os.stat(f1)), sig(os.stat(f2)) + if s1[0] <> 8 or s2[0] <> 8: + # 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) + try: + cs1, cs2, outcome = cache[key] + # cache hit + if s1 == cs1 and s2 == cs2: + # cached signatures match + return outcome + # stale cached signature(s) + except KeyError: + # cache miss + pass + # 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 - # 0-5: st_mode, st_ino, st_dev, st_nlink, st_uid, st_gid - # 6-9: st_size, st_atime, st_mtime, st_ctime - type = st[0] / 4096 - size = st[6] - mtime = st[8] - return type, size, mtime +def sig(st): + """Return signature (i.e., type, size, mtime) from raw stat data + 0-5: st_mode, st_ino, st_dev, st_nlink, st_uid, st_gid + 6-9: st_size, st_atime, st_mtime, st_ctime""" + type = st[0] / 4096 + size = st[6] + mtime = st[8] + return type, size, mtime -def do_cmp(f1, f2): # Compare two files, really - 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 +def do_cmp(f1, f2): + """Compare two files, really.""" + 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 |