mirror of
https://github.com/python/cpython.git
synced 2025-10-31 18:28:49 +00:00
63 lines
1.9 KiB
Python
63 lines
1.9 KiB
Python
"""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
|
|
"""
|
|
|
|
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 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
|