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# Copyright (C) 2006 by Canonical Ltd
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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"""Classes to provide name-to-object registry-like support."""
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class _ObjectGetter(object):
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"""Maintain a reference to an object, and return the object on request.
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This is used by Registry to make plain objects function similarly
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to lazily imported objects.
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Objects can be any sort of python object (class, function, module,
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def __init__(self, obj):
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"""Get the object that was saved at creation time"""
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class _LazyObjectGetter(_ObjectGetter):
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"""Keep a record of a possible object.
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When requested, load and return it.
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__slots__ = ['_module_name', '_member_name', '_imported']
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def __init__(self, module_name, member_name):
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self._module_name = module_name
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self._member_name = member_name
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self._imported = False
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super(_LazyObjectGetter, self).__init__(None)
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"""Get the referenced object.
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Upon first request, the object will be imported. Future requests will
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return the imported object.
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if not self._imported:
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return super(_LazyObjectGetter, self).get_obj()
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obj = __import__(self._module_name, globals(), locals(),
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obj = getattr(obj, self._member_name)
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class Registry(object):
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"""A class that registers objects to a name.
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There are many places that want to collect related objects and access them
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by a key. This class is designed to allow registering the mapping from key
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to object. It goes one step further, and allows registering a name to a
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hypothetical object which has not been imported yet. It also supports
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adding additional information at registration time so that decisions can be
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made without having to import the object (which may be expensive).
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The functions 'get', 'get_info', and 'get_help' also support a
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'default_key' (settable through my_registry.default_key = XXX, XXX must
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already be registered.) Calling my_registry.get() or my_registry.get(None),
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will return the entry for the default key.
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"""Create a new Registry."""
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self._default_key = None
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# Map from key => (is_lazy, info)
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def register(self, key, obj, help=None, info=None,
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override_existing=False):
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"""Register a new object to a name.
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:param key: This is the key to use to request the object later.
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:param obj: The object to register.
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:param help: Help text for this entry. This may be a string or
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a callable. If it is a callable, it should take two
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parameters (registry, key): this registry and the key that
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the help was registered under.
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:param info: More information for this entry. Registry.get_info()
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can be used to get this information. Registry treats this as an
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opaque storage location (it is defined by the caller).
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:param override_existing: Raise KeyErorr if False and something has
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already been registered for that key. If True, ignore if there
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is an existing key (always register the new value).
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if not override_existing:
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if key in self._dict:
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raise KeyError('Key %r already registered' % key)
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self._dict[key] = _ObjectGetter(obj)
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self._add_help_and_info(key, help=help, info=info)
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def register_lazy(self, key, module_name, member_name,
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help=None, info=None,
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override_existing=False):
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"""Register a new object to be loaded on request.
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:param module_name: The python path to the module. Such as 'os.path'.
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:param member_name: The member of the module to return. If empty or
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None, get() will return the module itself.
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:param help: Help text for this entry. This may be a string or
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:param info: More information for this entry. Registry
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:param override_existing: If True, replace the existing object
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with the new one. If False, if there is already something
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registered with the same key, raise a KeyError
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if not override_existing:
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if key in self._dict:
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raise KeyError('Key %r already registered' % key)
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self._dict[key] = _LazyObjectGetter(module_name, member_name)
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self._add_help_and_info(key, help=help, info=info)
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def _add_help_and_info(self, key, help=None, info=None):
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"""Add the help and information about this key"""
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self._help_dict[key] = help
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self._info_dict[key] = info
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def get(self, key=None):
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"""Return the object register()'ed to the given key.
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May raise ImportError if the object was registered lazily and
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there are any problems, or AttributeError if the module does not
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have the supplied member.
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:param key: The key to obtain the object for. If no object has been
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registered to that key, the object registered for self.default_key
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will be returned instead, if it exists. Otherwise KeyError will be
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:return: The previously registered object.
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:raises ImportError: If the object was registered lazily, and there are
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problems during import.
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:raises AttributeError: If registered lazily, and the module does not
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contain the registered member.
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return self._dict[self._get_key_or_default(key)].get_obj()
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def _get_key_or_default(self, key=None):
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"""Return either 'key' or the default key if key is None"""
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if self.default_key is None:
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raise KeyError('Key is None, and no default key is set')
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return self.default_key
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def get_help(self, key=None):
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"""Get the help text associated with the given key"""
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the_help = self._help_dict[self._get_key_or_default(key)]
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if callable(the_help):
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return the_help(self, key)
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def get_info(self, key=None):
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"""Get the extra information associated with the given key"""
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return self._info_dict[self._get_key_or_default(key)]
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def remove(self, key):
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"""Remove a registered entry.
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This is mostly for the test suite, but it can be used by others
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def __contains__(self, key):
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return key in self._dict
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"""Get a list of registered entries"""
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return sorted(self._dict.keys())
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for key, getter in self._dict.iteritems():
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yield key, getter.get_obj()
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def _set_default_key(self, key):
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if not self._dict.has_key(key):
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raise KeyError('No object registered under key %s.' % key)
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self._default_key = key
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def _get_default_key(self):
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return self._default_key
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default_key = property(_get_default_key, _set_default_key,
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doc="Current value of the default key."
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" Can be set to any existing key.")
added
removed
bzrlib/registry.py
