Lib/statcache.py

   1 # Module 'statcache'
   2 #
   3 # Maintain a cache of file stats.
   4 # There are functions to reset the cache or to selectively remove items.
   5
   6 import os
   7 from stat import *
   8
   9 # The cache.
  10 # Keys are pathnames, values are `os.stat' outcomes.
  11 #
  12 cache = {}
  13
  14
  15 # Stat a file, possibly out of the cache.
  16 #
  17 def stat(path):
  18         if cache.has_key(path):
  19                 return cache[path]
  20         cache[path] = ret = os.stat(path)
  21         return ret
  22
  23
  24 # Reset the cache completely.
  25 # Hack: to reset a global variable, we import this module.
  26 #
  27 def reset():
  28         import statcache
  29         # Check that we really imported the same module
  30         if cache is not statcache.cache:
  31                 raise 'sorry, statcache identity crisis'
  32         statcache.cache = {}
  33
  34
  35 # Remove a given item from the cache, if it exists.
  36 #
  37 def forget(path):
  38         if cache.has_key(path):
  39                 del cache[path]
  40
  41
  42 # Remove all pathnames with a given prefix.
  43 #
  44 def forget_prefix(prefix):
  45         n = len(prefix)
  46         for path in cache.keys():
  47                 if path[:n] == prefix:
  48                         del cache[path]
  49
  50
  51 # Forget about a directory and all entries in it, but not about
  52 # entries in subdirectories.
  53 #
  54 def forget_dir(prefix):
  55         if prefix[-1:] == '/' and prefix <> '/':
  56                 prefix = prefix[:-1]
  57         forget(prefix)
  58         if prefix[-1:] <> '/':
  59                 prefix = prefix + '/'
  60         n = len(prefix)
  61         for path in cache.keys():
  62                 if path[:n] == prefix:
  63                         rest = path[n:]
  64                         if rest[-1:] == '/': rest = rest[:-1]
  65                         if '/' not in rest:
  66                                 del cache[path]
  67
  68
  69 # Remove all pathnames except with a given prefix.
  70 # Normally used with prefix = '/' after a chdir().
  71 #
  72 def forget_except_prefix(prefix):
  73         n = len(prefix)
  74         for path in cache.keys():
  75                 if path[:n] <> prefix:
  76                         del cache[path]
  77
  78
  79 # Check for directory.
  80 #
  81 def isdir(path):
  82         try:
  83                 st = stat(path)
  84         except os.error:
  85                 return 0
  86         return S_ISDIR(st[ST_MODE])