30: Added plugable module with more generic implementation of Registrar; added corresponding unit tests

1 files changed, 95 insertions, 0 deletions

diff --git a/ipalib/plugable.py b/ipalib/plugable.py
new file mode 100644
index 00000000..ba2241b9
--- /dev/null
+++ b/ipalib/plugable.py
@@ -0,0 +1,95 @@
+# Authors:
+#   Jason Gerard DeRose <jderose@redhat.com>
+#
+# Copyright (C) 2008  Red Hat
+# see file 'COPYING' for use and warranty information
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation; version 2 only
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+"""
+Utility classes for registering plugins, base classe for writing plugins.
+"""
+
+import inspect
+import exceptions
+
+
+
+class Registrar(object):
+	def __init__(self, *allowed):
+		"""
+		`*allowed` is a list of the base classes plugins can be subclassed
+		from.
+		"""
+		self.__allowed = frozenset(allowed)
+		self.__d = {}
+		self.__registered = set()
+		assert len(self.__allowed) == len(allowed)
+		for base in self.__allowed:
+			assert inspect.isclass(base)
+			assert base.__name__ not in self.__d
+			self.__d[base.__name__] = {}
+
+	def __findbase(self, cls):
+		"""
+		If `cls` is a subclass of a base in self.__allowed, returns that
+		base; otherwise raises SubclassError.
+		"""
+		assert inspect.isclass(cls)
+		for base in self.__allowed:
+			if issubclass(cls, base):
+				return base
+		raise exceptions.SubclassError(cls, self.__allowed)
+
+	def __call__(self, cls, override=False):
+		"""
+		Register the plugin `cls`.
+		"""
+		if not inspect.isclass(cls):
+			raise TypeError('plugin must be a class: %r'  % cls)
+
+		# Find the base class or raise SubclassError:
+		base = self.__findbase(cls)
+		sub_d = self.__d[base.__name__]
+
+		# Raise DuplicateError if this exact class was already registered:
+		if cls in self.__registered:
+			raise exceptions.DuplicateError(cls)
+
+		# Check override:
+		if cls.__name__ in sub_d:
+			# Must use override=True to override:
+			if not override:
+				raise exceptions.OverrideError(base, cls)
+		else:
+			# There was nothing already registered to override:
+			if override:
+				raise exceptions.MissingOverrideError(base, cls)
+
+		# The plugin is okay, add to __registered and sub_d:
+		self.__registered.add(cls)
+		sub_d[cls.__name__] = cls
+
+	def __getitem__(self, name):
+		"""
+		Returns a copy of the namespace dict of the base class named `name`.
+		"""
+		return dict(self.__d[name])
+
+	def __iter__(self):
+		"""
+		Iterates through the names of the allowed base classes.
+		"""
+		for key in self.__d:
+			yield key