Lib/statcache.py

   1 """Maintain a cache of stat() information on files.
   2
   3 There are functions to reset the cache or to selectively remove items.
   4 """
   5
   6 import warnings
   7 warnings.warn("The statcache module is obsolete.  Use os.stat() instead.",
   8               DeprecationWarning)
   9 del warnings
  10
  11 import os as _os
  12 from stat import *
  13
  14 __all__ = ["stat","reset","forget","forget_prefix","forget_dir",
  15            "forget_except_prefix","isdir"]
  16
  17 # The cache.  Keys are pathnames, values are os.stat outcomes.
  18 # Remember that multiple threads may be calling this!  So, e.g., that
  19 # path in cache returns 1 doesn't mean the cache will still contain
  20 # path on the next line.  Code defensively.
  21
  22 cache = {}
  23
  24 def stat(path):
  25     """Stat a file, possibly out of the cache."""
  26     ret = cache.get(path, None)
  27     if ret is None:
  28         cache[path] = ret = _os.stat(path)
  29     return ret
  30
  31 def reset():
  32     """Clear the cache."""
  33     cache.clear()
  34
  35 # For thread saftey, always use forget() internally too.
  36 def forget(path):
  37     """Remove a given item from the cache, if it exists."""
  38     try:
  39         del cache[path]
  40     except KeyError:
  41         pass
  42
  43 def forget_prefix(prefix):
  44     """Remove all pathnames with a given prefix."""
  45     for path in cache.keys():
  46         if path.startswith(prefix):
  47             forget(path)
  48
  49 def forget_dir(prefix):
  50     """Forget a directory and all entries except for entries in subdirs."""
  51
  52     # Remove trailing separator, if any.  This is tricky to do in a
  53     # x-platform way.  For example, Windows accepts both / and \ as
  54     # separators, and if there's nothing *but* a separator we want to
  55     # preserve that this is the root.  Only os.path has the platform
  56     # knowledge we need.
  57     from os.path import split, join
  58     prefix = split(join(prefix, "xxx"))[0]
  59     forget(prefix)
  60     for path in cache.keys():
  61         # First check that the path at least starts with the prefix, so
  62         # that when it doesn't we can avoid paying for split().
  63         if path.startswith(prefix) and split(path)[0] == prefix:
  64             forget(path)
  65
  66 def forget_except_prefix(prefix):
  67     """Remove all pathnames except with a given prefix.
  68
  69     Normally used with prefix = '/' after a chdir().
  70     """
  71
  72     for path in cache.keys():
  73         if not path.startswith(prefix):
  74             forget(path)
  75
  76 def isdir(path):
  77     """Return True if directory, else False."""
  78     try:
  79         st = stat(path)
  80     except _os.error:
  81         return False
  82     return S_ISDIR(st.st_mode)