Lib/filecmp.py

   1 """Compare files."""
   2
   3 import os, stat, statcache
   4
   5 _cache = {}
   6 BUFSIZE=8*1024
   7
   8 def cmp(f1, f2, shallow=1,use_statcache=0):
   9         """Compare two files.
  10
  11         Arguments:
  12
  13         f1 -- First file name
  14
  15         f2 -- Second file name
  16
  17         shallow -- Just check stat signature (do not read the files).
  18                    defaults to 1.
  19
  20         use_statcache -- Do not stat() each file directly: go through
  21                          the statcache module for more efficiency.
  22
  23         Return value:
  24
  25         integer -- 1 if the files are the same, 0 otherwise.
  26
  27         This function uses a cache for past comparisons and the results,
  28         with a cache invalidation mechanism relying on stale signatures.
  29         Of course, if 'use_statcache' is true, this mechanism is defeated,
  30         and the cache will never grow stale.
  31
  32         """
  33         stat_function = (os.stat, statcache.stat)[use_statcache]
  34         s1, s2 = _sig(stat_function(f1)), _sig(stat_function(f2))
  35         if s1[0]!=stat.S_IFREG or s2[0]!=stat.S_IFREG: return 0
  36         if shallow and s1 == s2: return 1
  37         if s1[1]!=s2[1]:         return 0
  38
  39         result = _cache.get((f1, f2))
  40         if result and (s1, s2)==result[:2]:
  41                 return result[2]
  42         outcome = _do_cmp(f1, f2)
  43         _cache[f1, f2] = s1, s2, outcome
  44         return outcome
  45
  46 def _sig(st):
  47         return (stat.S_IFMT(st[stat.ST_MODE]),
  48                 st[stat.ST_SIZE],
  49                 st[stat.ST_MTIME])
  50
  51 def _do_cmp(f1, f2):
  52         bufsize = BUFSIZE
  53         fp1 , fp2 = open(f1, 'rb'), open(f2, 'rb')
  54         while 1:
  55                 b1, b2 = fp1.read(bufsize), fp2.read(bufsize)
  56                 if b1!=b2: return 0
  57                 if not b1: return 1