mirror of
https://github.com/python/cpython.git
synced 2024-11-24 17:47:13 +01:00
75 lines
2.1 KiB
Python
75 lines
2.1 KiB
Python
|
# 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
|
||
|
|
#
|
||
|
|
# XXX There is a dependency on constants in <sys/stat.h> here.
|
||
|
|
|
||
|
|
import posix
|
||
|
|
import statcache
|
||
|
|
|
||
|
|
|
||
|
|
# The cache.
|
||
|
|
#
|
||
|
|
cache = {}
|
||
|
|
|
||
|
|
|
||
|
|
# Compare two files, use the cache if possible.
|
||
|
|
# May raise posix.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 s1[0] <> 8 or s2[0] <> 8: # XXX 8 is S_IFREG in <sys/stat.h>
|
||
|
|
# 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):
|
||
|
|
# 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 # XXX dependent on S_IFMT in <sys/stat.h>
|
||
|
|
size = st[6]
|
||
|
|
mtime = st[8]
|
||
|
|
return type, size, mtime
|
||
|
|
|
||
|
|
# Compare two files, really.
|
||
|
|
#
|
||
|
|
def do_cmp(f1, f2):
|
||
|
|
#print ' cmp', f1, f2 # XXX remove when debugged
|
||
|
|
bufsize = 8096 # 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
|