| # Module 'cmp' |
| |
| # 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):# 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]<>8or s2[0]<>8: |
| # Either is a not a plain file -- always report as different |
| return0 |
| if s1== s2: |
| # type, size & mtime match -- report same |
| return1 |
| if s1[:2]<> s2[:2]:# Types or sizes differ, don't bother |
| # types or sizes differ -- report different |
| return0 |
| # same type and size -- look in the cache |
| key= f1+' '+ f2 |
| try: |
| cs1, cs2, outcome= cache[key] |
| # cache hit |
| if s1== cs1and s2== cs2: |
| # cached signatures match |
| return outcome |
| # stale cached signature(s) |
| exceptKeyError: |
| # 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=8096# Could be tuned |
| fp1= open(f1,'r') |
| fp2= open(f2,'r') |
| while1: |
| b1= fp1.read(bufsize) |
| b2= fp2.read(bufsize) |
| if b1<> b2:return0 |
| ifnot b1:return1 |
