Add @lazy_property decorator

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

diff --git a/Makefile.am b/Makefile.am
index 64494a308a919f16677fe8866d70f3aa2ff32b18..cd87e46388e6dcc973c7db56969931d5a2a7498f 100644 (file)
--- a/Makefile.am
+++ b/Makefile.am
@@ -79,6 +79,7 @@ buildservice_PYTHON = \
        src/buildservice/cache.py \
        src/buildservice/constants.py \
        src/buildservice/database.py \
+       src/buildservice/decorators.py \
        src/buildservice/distribution.py \
        src/buildservice/git.py \
        src/buildservice/__init__.py \

diff --git a/src/buildservice/decorators.py b/src/buildservice/decorators.py
new file mode 100644 (file)
index 0000000..d6d948e
--- /dev/null
+++ b/src/buildservice/decorators.py
@@ -0,0 +1,41 @@
+#!/usr/bin/python
+
+class lazy_property(property):
+       """
+               The property is only computed once and then being
+               cached until the end of the lifetime of the object.
+       """
+       def __init__(self, fget, fset=None, fdel=None, doc=None):
+               property.__init__(self, fget=fget, fset=fset, fdel=fdel, doc=doc)
+
+               # Make a cache key
+               self._name = "_cache_%s" % self.fget.__name__
+
+       def __get__(self, instance, owner):
+               if instance is None:
+                       return self
+
+               if hasattr(instance, self._name):
+                       result = getattr(instance, self._name)
+               else:
+                       if not self.fget is None:
+                               result = self.fget(instance)
+
+                       setattr(instance, self._name, result)
+
+               return result
+
+       def __set__(self, instance, value):
+               if instance is None:
+                       raise AttributeError
+
+               if self.fset is None:
+                       setattr(instance, self._name, value)
+               else:
+                       self.fset(instance, value)
+
+                       # Remove any cached attributes
+                       try:
+                               delattr(instance, self._name)
+                       except AttributeError:
+                               pass