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"""Maintain a cache of stat() information on files.
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There are functions to reset the cache or to selectively remove items.
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"""
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import os as _os
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from stat import *
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__all__ = ["stat","reset","forget","forget_prefix","forget_dir",
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"forget_except_prefix","isdir"]
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# The cache. Keys are pathnames, values are os.stat outcomes.
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# Remember that multiple threads may be calling this! So, e.g., that
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# cache.has_key(path) returns 1 doesn't mean the cache will still contain
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# path on the next line. Code defensively.
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cache = {}
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def stat(path):
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"""Stat a file, possibly out of the cache."""
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ret = cache.get(path, None)
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if ret is None:
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cache[path] = ret = _os.stat(path)
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return ret
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def reset():
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"""Clear the cache."""
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cache.clear()
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# For thread saftey, always use forget() internally too.
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def forget(path):
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"""Remove a given item from the cache, if it exists."""
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try:
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del cache[path]
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except KeyError:
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pass
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def forget_prefix(prefix):
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"""Remove all pathnames with a given prefix."""
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for path in cache.keys():
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if path.startswith(prefix):
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forget(path)
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def forget_dir(prefix):
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"""Forget a directory and all entries except for entries in subdirs."""
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# Remove trailing separator, if any. This is tricky to do in a
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# x-platform way. For example, Windows accepts both / and \ as
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# separators, and if there's nothing *but* a separator we want to
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# preserve that this is the root. Only os.path has the platform
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# knowledge we need.
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from os.path import split, join
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prefix = split(join(prefix, "xxx"))[0]
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forget(prefix)
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for path in cache.keys():
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# First check that the path at least starts with the prefix, so
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# that when it doesn't we can avoid paying for split().
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if path.startswith(prefix) and split(path)[0] == prefix:
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forget(path)
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def forget_except_prefix(prefix):
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"""Remove all pathnames except with a given prefix.
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Normally used with prefix = '/' after a chdir().
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"""
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for path in cache.keys():
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if not path.startswith(prefix):
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forget(path)
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def isdir(path):
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"""Return 1 if directory, else 0."""
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try:
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st = stat(path)
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except _os.error:
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return 0
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return S_ISDIR(st[ST_MODE])
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