Refactor infra git libs and testing.

infra/libs/decorators/decorators.py

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import functools
+
+
+class cached_property(object):
+  """Like @property, except that the result of get is cached on
+  self.{'_' + fn.__name__}.
+
+  NOTE: This implementation is not threadsafe.
+
+  >>> class Test(object):
+  ...  @cached_property
+  ...  def foo(self):
+  ...   print "hello"
+  ...   return 10
+  ...
+  >>> t = Test()
+  >>> t.foo
+  hello
+  10
+  >>> t.foo
+  10
+  >>> t.foo = 20
+  >>> t.foo
+  20
+  >>> del t.foo
+  >>> t.foo
+  hello
+  10
+  >>>
+  """
+  def __init__(self, fn):
+    self.func = fn
+    self._iname = "_" + fn.__name__
+    functools.update_wrapper(self, fn)
+
+  def __get__(self, inst, cls=None):
+    if inst is None:
+      return self
+    if not hasattr(inst, self._iname):
+      val = self.func(inst)
+      # Some methods call out to another layer to calculate the value. This
+      # higher layer will assign directly to the property, so we have to do
+      # the extra hasattr here to determine if the value has been set as a side
+      # effect of func()
+      if not hasattr(inst, self._iname):
+        setattr(inst, self._iname, val)
+    return getattr(inst, self._iname)
+
+  def __delete__(self, inst):
+    assert inst is not None
+    if hasattr(inst, self._iname):
+      delattr(inst, self._iname)