Make 'persistent'/'BTrees' soft dependencies.

- 'persistent' is used only for doctests.

- If 'BTrees' is not importable ('OOBTree' used for attribute storage),
  fall back to using 'dict'.

- Both are installable via the 'zope.annotation[btree]' extra.

- Closes LP #878265.

CHANGES.rst

@@ -1,10 +1,17 @@
 Changes
 =======
 
-4.3.1 (unreleased)
+4.4.0 (unreleased)
 ------------------
 
-- TBD
+- LP #878265:
+
+  - Make ``persistent`` (used only for doctests) a soft dependency,
+    installable via the ``zope.annotation[btree]`` extra.
+
+  - Make ``BTrees`` (used for attribute storage) a soft dependency,
+    installable via the ``zope.annotation[btree]`` extra.  Fall back to
+    using ``dict`` for attribute storage if ``BTrees`` is not importable.
 
 4.3.0 (2014-12-26)
 ------------------

setup.py

@@ -42,7 +42,7 @@ def alltests():
 
 setup(
     name='zope.annotation',
-    version='4.3.1.dev0',
+    version='4.4.0.dev0',
     url='http://pypi.python.org/pypi/zope.annotation',
     license='ZPL 2.1',
     description='Object annotation mechanism',
@@ -76,15 +76,17 @@ def alltests():
     package_dir={'': 'src'},
     namespace_packages=['zope',],
     install_requires=[
-        'persistent',
-        'BTrees',
         'setuptools',
         'zope.interface',
         'zope.component',
         'zope.location',
         'zope.proxy',
         ],
     extras_require=dict(
+        btrees=[
+            'BTrees',
+            'persistent',
+        ],
         test=[
             'zope.testing'
             ],

src/zope/annotation/README.txt

@@ -15,7 +15,11 @@ First, let's make a persistent object we can create annotations for:
   >>> class IFoo(interface.Interface):
   ...     pass
   >>> from zope.annotation.interfaces import IAttributeAnnotatable
-  >>> from persistent import Persistent
+  >>> try:
+  ...     from persistent import Persistent
+  ... except ImportError:
+  ...     class Persistent(object):
+  ...         pass
   >>> @interface.implementer(IFoo, IAttributeAnnotatable)
   ... class Foo(Persistent):
   ...     pass

src/zope/annotation/attribute.py

@@ -12,7 +12,16 @@
 #
 ##############################################################################
 """Attribute Annotations implementation"""
-from BTrees.OOBTree import OOBTree
+import logging
+
+try:
+    from BTrees.OOBTree import OOBTree
+except ImportError:
+    logging.getLogger(__name__).warn(
+        'BTrees not available: falling back to dict for attribute storage')
+    _STORAGE = dict
+else:
+    _STORAGE = OOBTree
 
 from zope import component, interface
 from zope.annotation import interfaces
@@ -80,7 +89,7 @@ def __setitem__(self, key, value):
         try:
             annotations = self.obj.__annotations__
         except AttributeError:
-            annotations = self.obj.__annotations__ = OOBTree()
+            annotations = self.obj.__annotations__ = _STORAGE()
 
         annotations[key] = value
 

tox.ini

@@ -2,8 +2,8 @@
 envlist =
 #   PyPy3 support is pending release of a fix for:
 #   https://bitbucket.org/pypy/pypy/issue/1946
-#   py26,py27,py33,py34,pypy,pypy3,coverage
-    py26,py27,py33,py34,pypy,coverage
+#   py26,py27,py33,py34,pypy,pypy3,coverage,nobtree
+    py26,py27,py33,py34,pypy,coverage,nobtree
 
 [base]
 deps =
@@ -24,6 +24,15 @@ deps =
     BTrees
     persistent
 
+[testenv:nobtree]
+basepython =
+    python2.7
+commands =
+    python setup.py test -q
+# without explicit deps, setup.py test will download a bunch of eggs into $PWD
+deps =
+    {[base]deps}
+
 [testenv:coverage]
 basepython =
     python2.7