[Assorted-commits] SF.net SVN: assorted: [688] python-commons/trunk/src/commons/files.py

[<yan...@us...>]

Revision: 688
          http://assorted.svn.sourceforge.net/assorted/?rev=688&view=rev
Author:   yangzhang
Date:     2008-04-28 22:18:57 -0700 (Mon, 28 Apr 2008)

Log Message:
-----------
added versioned_guard, versioned_cache

Modified Paths:
--------------
    python-commons/trunk/src/commons/files.py

Modified: python-commons/trunk/src/commons/files.py
===================================================================
--- python-commons/trunk/src/commons/files.py	2008-04-29 00:32:42 UTC (rev 687)
+++ python-commons/trunk/src/commons/files.py	2008-04-29 05:18:57 UTC (rev 688)
@@ -14,7 +14,7 @@
 from __future__ import with_statement
 
 import os, re, tempfile
-
+from cPickle import *
 from path import path
 
 def soft_makedirs( path ):
@@ -113,3 +113,59 @@
     def close( self ):
         self.reader.close()
         self.writer.close()
+
+def versioned_guard(path, fresh_version):
+    """
+    Maintain a version object.  This is useful for working with versioned
+    caches.
+
+    @param path: The path to the file containing the cached version object.
+    @type path: str
+
+    @param fresh_version: The actual latest version that the cached version
+    should be compared against.
+    @type fresh_version: object (any type that can be compared)
+
+    @return: True iff the cached version is obsolete (less than the fresh
+    version or doesn't exist).
+    @rtype: bool
+    """
+    try:
+        with file( path ) as f: cache_version = load(f)
+    except IOError, (errno, errstr):
+        if errno != 2: raise
+        return True
+    else:
+        if fresh_version > cache_version:
+            with file( path, 'w' ) as f: dump(fresh_version, f)
+            return True
+        else:
+            return False
+
+def versioned_cache(version_path, fresh_version, cache_path, cache_func):
+    """
+    If fresh_version is newer than the version in version_path, then invoke
+    cache_func and cache the result in cache_path (using pickle).
+
+    @param version_path: The path to the file version.
+    @type version_path: str
+
+    @param fresh_version: The actual, up-to-date version value.
+    @type fresh_version: object (any type that can be compared)
+
+    @param cache_path: The path to the cached data.
+    @type cache_path: str
+
+    @param cache_func: The function that produces the fresh data to be cached.
+    @type cache_func: function (no arguments)
+    """
+    if versioned_guard( version_path, fresh_version ):
+        # cache obsolete, force-fetch new data
+        print 'here'
+        result = cache_func()
+        with file(cache_path, 'w') as f: dump(result, f)
+        return result
+    else:
+        # cache up-to-date (should be available since dlcs-timestamp exists!)
+        print 'there'
+        with file(cache_path) as f: return load(f)


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