Added cached_property to utils.

LICENSE

@@ -75,3 +75,33 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */
+
+utils.cached_property extracted from Celery
+-------------------------------------------
+Copyright (c) 2009-2011, Ask Solem and contributors.
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright notice,
+      this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in the
+      documentation and/or other materials provided with the distribution.
+
+Neither the name of Ask Solem nor the names of its contributors may be used
+to endorse or promote products derived from this software without specific
+prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
+BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.

compressor/utils.py

@@ -192,3 +192,70 @@ class AppSettings(object):
 
    def issetting(self, (name, value)):
        return name == name.upper()
+
+
+class cached_property(object):
+   """Property descriptor that caches the return value
+   of the get function.
+
+   *Examples*
+
+   .. code-block:: python
+
+       @cached_property
+       def connection(self):
+           return Connection()
+
+       @connection.setter  # Prepares stored value
+       def connection(self, value):
+           if value is None:
+               raise TypeError("Connection must be a connection")
+           return value
+
+       @connection.deleter
+       def connection(self, value):
+           # Additional action to do at del(self.attr)
+           if value is not None:
+               print("Connection %r deleted" % (value, ))
+   """
+
+   def __init__(self, fget=None, fset=None, fdel=None, doc=None):
+       self.__get = fget
+       self.__set = fset
+       self.__del = fdel
+       self.__doc__ = doc or fget.__doc__
+       self.__name__ = fget.__name__
+       self.__module__ = fget.__module__
+
+   def __get__(self, obj, type=None):
+       if obj is None:
+           return self
+       try:
+           return obj.__dict__[self.__name__]
+       except KeyError:
+           value = obj.__dict__[self.__name__] = self.__get(obj)
+           return value
+
+   def __set__(self, obj, value):
+       if obj is None:
+           return self
+       if self.__set is not None:
+           value = self.__set(obj, value)
+       obj.__dict__[self.__name__] = value
+
+   def __delete__(self, obj):
+       if obj is None:
+           return self
+       try:
+           value = obj.__dict__.pop(self.__name__)
+       except KeyError:
+           pass
+       else:
+           if self.__del is not None:
+               self.__del(obj, value)
+
+   def setter(self, fset):
+       return self.__class__(self.__get, fset, self.__del)
+
+   def deleter(self, fdel):
+       return self.__class__(self.__get, self.__set, fdel)