From: Michael Tremer <michael.tremer@ipfire.org>
Date: Fri, 6 Oct 2017 15:49:01 +0000 (+0100)
Subject: Add @lazy_property decorator
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=012035e093e37b34d3b8cf9d421cbaf99aa61f91;p=pbs.git

Add @lazy_property decorator

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

diff --git a/Makefile.am b/Makefile.am
index 64494a30..cd87e463 100644
--- 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
index 00000000..d6d948e7
--- /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