Add pylint to depot_tools.

third_party/logilab/common/cache.py

+# copyright 2003-2011 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
+# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
+#
+# This file is part of logilab-common.
+#
+# logilab-common is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation, either version 2.1 of the License, or (at your option) any
+# later version.
+#
+# logilab-common is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Lesser General Public License along
+# with logilab-common.  If not, see <http://www.gnu.org/licenses/>.
+"""Cache module, with a least recently used algorithm for the management of the
+deletion of entries.
+
+
+
+
+"""
+__docformat__ = "restructuredtext en"
+
+from threading import Lock
+
+from logilab.common.decorators import locked
+
+_marker = object()
+
+class Cache(dict):
+    """A dictionary like cache.
+
+    inv:
+        len(self._usage) <= self.size
+        len(self.data) <= self.size
+    """
+
+    def __init__(self, size=100):
+        """ Warning : Cache.__init__() != dict.__init__().
+        Constructor does not take any arguments beside size.
+        """
+        assert size >= 0, 'cache size must be >= 0 (0 meaning no caching)'
+        self.size = size
+        self._usage = []
+        self._lock = Lock()
+        super(Cache, self).__init__()
+
+    def _acquire(self):
+        self._lock.acquire()
+
+    def _release(self):
+        self._lock.release()
+
+    def _update_usage(self, key):
+        if not self._usage:
+            self._usage.append(key)
+        elif self._usage[-1] != key:
+            try:
+                self._usage.remove(key)
+            except ValueError:
+                # we are inserting a new key
+                # check the size of the dictionary
+                # and remove the oldest item in the cache
+                if self.size and len(self._usage) >= self.size:
+                    super(Cache, self).__delitem__(self._usage[0])
+                    del self._usage[0]
+            self._usage.append(key)
+        else:
+            pass # key is already the most recently used key
+
+    def __getitem__(self, key):
+        value = super(Cache, self).__getitem__(key)
+        self._update_usage(key)
+        return value
+    __getitem__ = locked(_acquire, _release)(__getitem__)
+
+    def __setitem__(self, key, item):
+        # Just make sure that size > 0 before inserting a new item in the cache
+        if self.size > 0:
+            super(Cache, self).__setitem__(key, item)
+            self._update_usage(key)
+    __setitem__ = locked(_acquire, _release)(__setitem__)
+
+    def __delitem__(self, key):
+        super(Cache, self).__delitem__(key)
+        self._usage.remove(key)
+    __delitem__ = locked(_acquire, _release)(__delitem__)
+
+    def clear(self):
+        super(Cache, self).clear()
+        self._usage = []
+    clear = locked(_acquire, _release)(clear)
+
+    def pop(self, key, default=_marker):
+        if key in self:
+            self._usage.remove(key)
+        #if default is _marker:
+        #    return super(Cache, self).pop(key)
+        return super(Cache, self).pop(key, default)
+    pop = locked(_acquire, _release)(pop)
+
+    def popitem(self):
+        raise NotImplementedError()
+
+    def setdefault(self, key, default=None):
+        raise NotImplementedError()
+
+    def update(self, other):
+        raise NotImplementedError()
+
+