Initial revision

Lib/statcache.py

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+# Module 'statcache'
+#
+# Maintain a cache of file stats.
+# There are functions to reset the cache or to selectively remove items.
+
+import posix
+
+
+# The cache.
+# Keys are pathnames, values are `posix.stat' outcomes.
+#
+cache = {}
+
+
+# Stat a file, possibly out of the cache.
+#
+def stat(path):
+	try:
+		return cache[path]
+	except RuntimeError:
+		pass
+	cache[path] = ret = posix.stat(path)
+	return ret
+
+
+# Reset the cache completely.
+# Hack: to reset a global variable, we import this module.
+#
+def reset():
+	import statcache
+	# Check that we really imported the same module
+	if cache is not statcache.cache:
+		raise 'sorry, statcache identity crisis'
+	statcache.cache = {}
+
+
+# Remove a given item from the cache, if it exists.
+#
+def forget(path):
+	try:
+		del cache[path]
+	except RuntimeError:
+		pass
+
+
+# Remove all pathnames with a given prefix.
+#
+def forget_prefix(prefix):
+	n = len(prefix)
+	for path in cache.keys():
+		if path[:n] = prefix:
+			del cache[path]
+
+
+# Forget about a directory and all entries in it, but not about
+# entries in subdirectories.
+#
+def forget_dir(prefix):
+	if prefix[-1:] = '/' and prefix <> '/':
+		prefix = prefix[:-1]
+	forget(prefix)
+	if prefix[-1:] <> '/':
+		prefix = prefix + '/'
+	n = len(prefix)
+	for path in cache.keys():
+		if path[:n] = prefix:
+			rest = path[n:]
+			if rest[-1:] = '/': rest = rest[:-1]
+			if '/' not in rest:
+				del cache[path]
+
+
+# Remove all pathnames except with a given prefix.
+# Normally used with prefix = '/' after a chdir().
+#
+def forget_except_prefix(prefix):
+	n = len(prefix)
+	for path in cache.keys():
+		if path[:n] <> prefix:
+			del cache[path]
+
+
+# Check for directory.
+#
+def isdir(path):
+	try:
+		# mode is st[0]; type is mode/4096; S_IFDIR is 4
+		return stat(path)[0] / 4096 = 4
+	except RuntimeError:
+		return 0