# copyright 2003-2013 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
# contact http://www.logilab.fr/ -- mailto:[email protected]
#
# This file is part of Logilab-common.
#
# Logilab-common is free software: you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by the
# Free Software Foundation, either version 2.1 of the License, or (at your
# option) any later version.
#
# Logilab-common 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 Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License along
# with Logilab-common. If not, see <http://www.gnu.org/licenses/>.
"""This module provides bases for predicates dispatching (the pattern in use
here is similar to what's refered as multi-dispatch or predicate-dispatch in the
literature, though a bit different since the idea is to select across different
implementation 'e.g. classes), not to dispatch a message to a function or
method. It contains the following classes:
* :class:`RegistryStore`, the top level object which loads implementation
objects and stores them into registries. You'll usually use it to access
registries and their contained objects;
* :class:`Registry`, the base class which contains objects semantically grouped
(for instance, sharing a same API, hence the 'implementation' name). You'll
use it to select the proper implementation according to a context. Notice you
may use registries on their own without using the store.
.. Note::
implementation objects are usually designed to be accessed through the
registry and not by direct instantiation, besides to use it as base classe.
The selection procedure is delegated to a selector, which is responsible for
scoring the object according to some context. At the end of the selection, if an
implementation has been found, an instance of this class is returned. A selector
is built from one or more predicates combined together using AND, OR, NOT
operators (actually `&`, `|` and `~`). You'll thus find some base classes to
build predicates:
* :class:`Predicate`, the abstract base predicate class
* :class:`AndPredicate`, :class:`OrPredicate`, :class:`NotPredicate`, which you
shouldn't have to use directly. You'll use `&`, `|` and '~' operators between
predicates directly
* :func:`objectify_predicate`
You'll eventually find one concrete predicate: :class:`yes`
.. autoclass:: RegistryStore
.. autoclass:: Registry
Predicates
----------
.. autoclass:: Predicate
.. autofunc:: objectify_predicate
.. autoclass:: yes
Debugging
---------
.. autoclass:: traced_selection
Exceptions
----------
.. autoclass:: RegistryException
.. autoclass:: RegistryNotFound
.. autoclass:: ObjectNotFound
.. autoclass:: NoSelectableObject
"""
from __future__ import print_function
__docformat__ = "restructuredtext en"
import sys
import types
import weakref
import traceback as tb
from os import listdir, stat
from os.path import join, isdir, exists
from logging import getLogger
from warnings import warn
from six import string_types, add_metaclass
from logilab.common.modutils import modpath_from_file
from logilab.common.logging_ext import set_log_methods
from logilab.common.decorators import classproperty
class RegistryException(Exception):
"""Base class for registry exception."""
class RegistryNotFound(RegistryException):
"""Raised when an unknown registry is requested.
This is usually a programming/typo error.
"""
class ObjectNotFound(RegistryException):
"""Raised when an unregistered object is requested.
This may be a programming/typo or a misconfiguration error.
"""
class NoSelectableObject(RegistryException):
"""Raised when no object is selectable for a given context."""
def __init__(self, args, kwargs, objects):
self.args = args
self.kwargs = kwargs
self.objects = objects
def __str__(self):
return ('args: %s, kwargs: %s\ncandidates: %s'
% (self.args, self.kwargs.keys(), self.objects))
def _modname_from_path(path, extrapath=None):
modpath = modpath_from_file(path, extrapath)
# omit '__init__' from package's name to avoid loading that module
# once for each name when it is imported by some other object
# module. This supposes import in modules are done as::
#
# from package import something
#
# not::
#
# from package.__init__ import something
#
# which seems quite correct.
if modpath[-1] == '__init__':
modpath.pop()
return '.'.join(modpath)
def _toload_info(path, extrapath, _toload=None):
"""Return a dictionary of <modname>: <modpath> and an ordered list of
(file, module name) to load
"""
if _toload is None:
assert isinstance(path, list)
_toload = {}, []
for fileordir in path:
if isdir(fileordir) and exists(join(fileordir, '__init__.py')):
subfiles = [join(fileordir, fname) for fname in listdir(fileordir)]
_toload_info(subfiles, extrapath, _toload)
elif fileordir[-3:] == '.py':
modname = _modname_from_path(fileordir, extrapath)
_toload[0][modname] = fileordir
_toload[1].append((fileordir, modname))
return _toload
class RegistrableObject(object):
"""This is the base class for registrable objects which are selected
according to a context.
:attr:`__registry__`
name of the registry for this object (string like 'views',
'templates'...). You may want to define `__registries__` directly if your
object should be registered in several registries.
:attr:`__regid__`
object's identifier in the registry (string like 'main',
'primary', 'folder_box')
:attr:`__select__`
class'selector
Moreover, the `__abstract__` attribute may be set to True to indicate that a
class is abstract and should not be registered.
You don't have to inherit from this class to put it in a registry (having
`__regid__` and `__select__` is enough), though this is needed for classes
that should be automatically registered.
"""
__registry__ = None
__regid__ = None
__select__ = None
__abstract__ = True # see doc snipppets below (in Registry class)
@classproperty
def __registries__(cls):
if cls.__registry__ is None:
return ()
return (cls.__registry__,)
class RegistrableInstance(RegistrableObject):
"""Inherit this class if you want instances of the classes to be
automatically registered.
"""
def __new__(cls, *args, **kwargs):
"""Add a __module__ attribute telling the module where the instance was
created, for automatic registration.
"""
obj = super(RegistrableInstance, cls).__new__(cls)
# XXX subclass must no override __new__
filepath = tb.extract_stack(limit=2)[0][0]
obj.__module__ = _modname_from_path(filepath)
return obj
class Registry(dict):
"""The registry store a set of implementations associated to identifier:
* to each identifier are associated a list of implementations
* to select an implementation of a given identifier, you should use one of the
:meth:`select` or :meth:`select_or_none` method
* to select a list of implementations for a context, you should use the
:meth:`possible_objects` method
* dictionary like access to an identifier will return the bare list of
implementations for this identifier.
To be usable in a registry, the only requirement is to have a `__select__`
attribute.
At the end of the registration process, the :meth:`__registered__`
method is called on each registered object which have them, given the
registry in which it's registered as argument.
Registration methods:
.. automethod: register
.. automethod: unregister
Selection methods:
.. automethod: select
.. automethod: select_or_none
.. automethod: possible_objects
.. automethod: object_by_id
"""
def __init__(self, debugmode):
super(Registry, self).__init__()
self.debugmode = debugmode
def __getitem__(self, name):
"""return the registry (list of implementation objects) associated to
this name
"""
try:
return super(Registry, self).__getitem__(name)
except KeyError:
exc = ObjectNotFound(name)
exc.__traceback__ = sys.exc_info()[-1]
raise exc
@classmethod
def objid(cls, obj):
"""returns a unique identifier for an object stored in the registry"""
return '%s.%s' % (obj.__module__, cls.objname(obj))
@classmethod
def objname(cls, obj):
"""returns a readable name for an object stored in the registry"""
return getattr(obj, '__name__', id(obj))
def initialization_completed(self):
"""call method __registered__() on registered objects when the callback
is defined"""
for objects in self.values():
for objectcls in objects:
registered = getattr(objectcls, '__registered__', None)
if registered:
registered(self)
if self.debugmode:
wrap_predicates(_lltrace)
def register(self, obj, oid=None, clear=False):
"""base method to add an object in the registry"""
assert not '__abstract__' in obj.__dict__, obj
assert obj.__select__, obj
oid = oid or obj.__regid__
assert oid, ('no explicit name supplied to register object %s, '
'which has no __regid__ set' % obj)
if clear:
objects = self[oid] = []
else:
objects = self.setdefault(oid, [])
assert not obj in objects, 'object %s is already registered' % obj
objects.append(obj)
def register_and_replace(self, obj, replaced):
"""remove <replaced> and register <obj>"""
# XXXFIXME this is a duplication of unregister()
# remove register_and_replace in favor of unregister + register
# or simplify by calling unregister then register here
if not isinstance(replaced, string_types):
replaced = self.objid(replaced)
# prevent from misspelling
assert obj is not replaced, 'replacing an object by itself: %s' % obj
registered_objs = self.get(obj.__regid__, ())
for index, registered in enumerate(registered_objs):
if self.objid(registered) == replaced:
del registered_objs[index]
break
else:
self.warning('trying to replace %s that is not registered with %s',
replaced, obj)
self.register(obj)
def unregister(self, obj):
"""remove object <obj> from this registry"""
objid = self.objid(obj)
oid = obj.__regid__
for registered in self.get(oid, ()):
# use self.objid() to compare objects because vreg will probably
# have its own version of the object, loaded through execfile
if self.objid(registered) == objid:
self[oid].remove(registered)
break
else:
self.warning('can\'t remove %s, no id %s in the registry',
objid, oid)
def all_objects(self):
"""return a list containing all objects in this registry.
"""
result = []
for objs in self.values():
result += objs
return result
# dynamic selection methods ################################################
def object_by_id(self, oid, *args, **kwargs):
"""return object with the `oid` identifier. Only one object is expected
to be found.
raise :exc:`ObjectNotFound` if there are no object with id `oid` in this
registry
raise :exc:`AssertionError` if there is more than one object there
"""
objects = self[oid]
assert len(objects) == 1, objects
return objects[0](*args, **kwargs)
def select(self, __oid, *args, **kwargs):
"""return the most specific object among those with the given oid
according to the given context.
raise :exc:`ObjectNotFound` if there are no object with id `oid` in this
registry
raise :exc:`NoSelectableObject` if no object can be selected
"""
obj = self._select_best(self[__oid], *args, **kwargs)
if obj is None:
raise NoSelectableObject(args, kwargs, self[__oid] )
return obj
def select_or_none(self, __oid, *args, **kwargs):
"""return the most specific object among those with the given oid
according to the given context, or None if no object applies.
"""
try:
return self._select_best(self[__oid], *args, **kwargs)
except ObjectNotFound:
return None
def possible_objects(self, *args, **kwargs):
"""return an iterator on possible objects in this registry for the given
context
"""
for objects in self.values():
obj = self._select_best(objects, *args, **kwargs)
if obj is None:
continue
yield obj
def _select_best(self, objects, *args, **kwargs):
"""return an instance of the most specific object according
to parameters
return None if not object apply (don't raise `NoSelectableObject` since
it's costly when searching objects using `possible_objects`
(e.g. searching for hooks).
"""
score, winners = 0, None
for obj in objects:
objectscore = obj.__select__(obj, *args, **kwargs)
if objectscore > score:
score, winners = objectscore, [obj]
elif objectscore > 0 and objectscore == score:
winners.append(obj)
if winners is None:
return None
if len(winners) > 1:
# log in production environement / test, error while debugging
msg = 'select ambiguity: %s\n(args: %s, kwargs: %s)'
if self.debugmode:
# raise bare exception in debug mode
raise Exception(msg % (winners, args, kwargs.keys()))
self.error(msg, winners, args, kwargs.keys())
# return the result of calling the object
return self.selected(winners[0], args, kwargs)
def selected(self, winner, args, kwargs):
"""override here if for instance you don't want "instanciation"
"""
return winner(*args, **kwargs)
# these are overridden by set_log_methods below
# only defining here to prevent pylint from complaining
info = warning = error = critical = exception = debug = lambda msg, *a, **kw: None
def obj_registries(cls, registryname=None):
"""return a tuple of registry names (see __registries__)"""
if registryname:
return (registryname,)
return cls.__registries__
class RegistryStore(dict):
"""This class is responsible for loading objects and storing them
in their registry which is created on the fly as needed.
It handles dynamic registration of objects and provides a
convenient api to access them. To be recognized as an object that
should be stored into one of the store's registry
(:class:`Registry`), an object must provide the following
attributes, used control how they interact with the registry:
:attr:`__registries__`
list of registry names (string like 'views', 'templates'...) into which
the object should be registered
:attr:`__regid__`
object identifier in the registry (string like 'main',
'primary', 'folder_box')
:attr:`__select__`
the object predicate selectors
Moreover, the :attr:`__abstract__` attribute may be set to `True`
to indicate that an object is abstract and should not be registered
(such inherited attributes not considered).
.. Note::
When using the store to load objects dynamically, you *always* have
to use **super()** to get the methods and attributes of the
superclasses, and not use the class identifier. If not, you'll get into
trouble at reload time.
For example, instead of writing::
class Thing(Parent):
__regid__ = 'athing'
__select__ = yes()
def f(self, arg1):
Parent.f(self, arg1)
You must write::
class Thing(Parent):
__regid__ = 'athing'
__select__ = yes()
def f(self, arg1):
super(Thing, self).f(arg1)
Controlling object registration
-------------------------------
Dynamic loading is triggered by calling the
:meth:`register_objects` method, given a list of directories to
inspect for python modules.
.. automethod: register_objects
For each module, by default, all compatible objects are registered
automatically. However if some objects come as replacement of
other objects, or have to be included only if some condition is
met, you'll have to define a `registration_callback(vreg)`
function in the module and explicitly register **all objects** in
this module, using the api defined below.
.. automethod:: RegistryStore.register_all
.. automethod:: RegistryStore.register_and_replace
.. automethod:: RegistryStore.register
.. automethod:: RegistryStore.unregister
.. Note::
Once the function `registration_callback(vreg)` is implemented in a
module, all the objects from this module have to be explicitly
registered as it disables the automatic object registration.
Examples:
.. sourcecode:: python
def registration_callback(store):
# register everything in the module except BabarClass
store.register_all(globals().values(), __name__, (BabarClass,))
# conditionally register BabarClass
if 'babar_relation' in store.schema:
store.register(BabarClass)
In this example, we register all application object classes defined in the module
except `BabarClass`. This class is then registered only if the 'babar_relation'
relation type is defined in the instance schema.
.. sourcecode:: python
def registration_callback(store):
store.register(Elephant)
# replace Babar by Celeste
store.register_and_replace(Celeste, Babar)
In this example, we explicitly register classes one by one:
* the `Elephant` class
* the `Celeste` to replace `Babar`
If at some point we register a new appobject class in this module, it won't be
registered at all without modification to the `registration_callback`
implementation. The first example will register it though, thanks to the call
to the `register_all` method.
Controlling registry instantiation
----------------------------------
The `REGISTRY_FACTORY` class dictionary allows to specify which class should
be instantiated for a given registry name. The class associated to `None`
key will be the class used when there is no specific class for a name.
"""
def __init__(self, debugmode=False):
super(RegistryStore, self).__init__()
self.debugmode = debugmode
def reset(self):
"""clear all registries managed by this store"""
# don't use self.clear, we want to keep existing subdictionaries
for subdict in self.values():
subdict.clear()
self._lastmodifs = {}
def __getitem__(self, name):
"""return the registry (dictionary of class objects) associated to
this name
"""
try:
return super(RegistryStore, self).__getitem__(name)
except KeyError:
exc = RegistryNotFound(name)
exc.__traceback__ = sys.exc_info()[-1]
raise exc
# methods for explicit (un)registration ###################################
# default class, when no specific class set
REGISTRY_FACTORY = {None: Registry}
def registry_class(self, regid):
"""return existing registry named regid or use factory to create one and
return it"""
try:
return self.REGISTRY_FACTORY[regid]
except KeyError:
return self.REGISTRY_FACTORY[None]
def setdefault(self, regid):
try:
return self[regid]
except RegistryNotFound:
self[regid] = self.registry_class(regid)(self.debugmode)
return self[regid]
def register_all(self, objects, modname, butclasses=()):
"""register registrable objects into `objects`.
Registrable objects are properly configured subclasses of
:class:`RegistrableObject`. Objects which are not defined in the module
`modname` or which are in `butclasses` won't be registered.
Typical usage is:
.. sourcecode:: python
store.register_all(globals().values(), __name__, (ClassIWantToRegisterExplicitly,))
So you get partially automatic registration, keeping manual registration
for some object (to use
:meth:`~logilab.common.registry.RegistryStore.register_and_replace` for
instance).
"""
assert isinstance(modname, string_types), \
'modname expected to be a module name (ie string), got %r' % modname
for obj in objects:
if self.is_registrable(obj) and obj.__module__ == modname and not obj in butclasses:
if isinstance(obj, type):
self._load_ancestors_then_object(modname, obj, butclasses)
else:
self.register(obj)
def register(self, obj, registryname=None, oid=None, clear=False):
"""register `obj` implementation into `registryname` or
`obj.__registries__` if not specified, with identifier `oid` or
`obj.__regid__` if not specified.
If `clear` is true, all objects with the same identifier will be
previously unregistered.
"""
assert not obj.__dict__.get('__abstract__'), obj
for registryname in obj_registries(obj, registryname):
registry = self.setdefault(registryname)
registry.register(obj, oid=oid, clear=clear)
self.debug("register %s in %s['%s']",
registry.objname(obj), registryname, oid or obj.__regid__)
self._loadedmods.setdefault(obj.__module__, {})[registry.objid(obj)] = obj
def unregister(self, obj, registryname=None):
"""unregister `obj` object from the registry `registryname` or
`obj.__registries__` if not specified.
"""
for registryname in obj_registries(obj, registryname):
registry = self[registryname]
registry.unregister(obj)
self.debug("unregister %s from %s['%s']",
registry.objname(obj), registryname, obj.__regid__)
def register_and_replace(self, obj, replaced, registryname=None):
"""register `obj` object into `registryname` or
`obj.__registries__` if not specified. If found, the `replaced` object
will be unregistered first (else a warning will be issued as it is
generally unexpected).
"""
for registryname in obj_registries(obj, registryname):
registry = self[registryname]
registry.register_and_replace(obj, replaced)
self.debug("register %s in %s['%s'] instead of %s",
registry.objname(obj), registryname, obj.__regid__,
registry.objname(replaced))
# initialization methods ###################################################
def init_registration(self, path, extrapath=None):
"""reset registry and walk down path to return list of (path, name)
file modules to be loaded"""
# XXX make this private by renaming it to _init_registration ?
self.reset()
# compute list of all modules that have to be loaded
self._toloadmods, filemods = _toload_info(path, extrapath)
# XXX is _loadedmods still necessary ? It seems like it's useful
# to avoid loading same module twice, especially with the
# _load_ancestors_then_object logic but this needs to be checked
self._loadedmods = {}
return filemods
def register_objects(self, path, extrapath=None):
"""register all objects found walking down <path>"""
# load views from each directory in the instance's path
# XXX inline init_registration ?
filemods = self.init_registration(path, extrapath)
for filepath, modname in filemods:
self.load_file(filepath, modname)
self.initialization_completed()
def initialization_completed(self):
"""call initialization_completed() on all known registries"""
for reg in self.values():
reg.initialization_completed()
def _mdate(self, filepath):
""" return the modification date of a file path """
try:
return stat(filepath)[-2]
except OSError:
# this typically happens on emacs backup files (.#foo.py)
self.warning('Unable to load %s. It is likely to be a backup file',
filepath)
return None
def is_reload_needed(self, path):
"""return True if something module changed and the registry should be
reloaded
"""
lastmodifs = self._lastmodifs
for fileordir in path:
if isdir(fileordir) and exists(join(fileordir, '__init__.py')):
if self.is_reload_needed([join(fileordir, fname)
for fname in listdir(fileordir)]):
return True
elif fileordir[-3:] == '.py':
mdate = self._mdate(fileordir)
if mdate is None:
continue # backup file, see _mdate implementation
elif "flymake" in fileordir:
# flymake + pylint in use, don't consider these they will corrupt the registry
continue
if fileordir not in lastmodifs or lastmodifs[fileordir] < mdate:
self.info('File %s changed since last visit', fileordir)
return True
return False
def load_file(self, filepath, modname):
""" load registrable objects (if any) from a python file """
from logilab.common.modutils import load_module_from_name
if modname in self._loadedmods:
return
self._loadedmods[modname] = {}
mdate = self._mdate(filepath)
if mdate is None:
return # backup file, see _mdate implementation
elif "flymake" in filepath:
# flymake + pylint in use, don't consider these they will corrupt the registry
return
# set update time before module loading, else we get some reloading
# weirdness in case of syntax error or other error while importing the
# module
self._lastmodifs[filepath] = mdate
# load the module
module = load_module_from_name(modname)
self.load_module(module)
def load_module(self, module):
"""Automatically handle module objects registration.
Instances are registered as soon as they are hashable and have the
following attributes:
* __regid__ (a string)
* __select__ (a callable)
* __registries__ (a tuple/list of string)
For classes this is a bit more complicated :
- first ensure parent classes are already registered
- class with __abstract__ == True in their local dictionary are skipped
- object class needs to have registries and identifier properly set to a
non empty string to be registered.
"""
self.info('loading %s from %s', module.__name__, module.__file__)
if hasattr(module, 'registration_callback'):
module.registration_callback(self)
else:
self.register_all(vars(module).values(), module.__name__)
def _load_ancestors_then_object(self, modname, objectcls, butclasses=()):
"""handle class registration according to rules defined in
:meth:`load_module`
"""
# backward compat, we used to allow whatever else than classes
if not isinstance(objectcls, type):
if self.is_registrable(objectcls) and objectcls.__module__ == modname:
self.register(objectcls)
return
# imported classes
objmodname = objectcls.__module__
if objmodname != modname:
# The module of the object is not the same as the currently
# worked on module, or this is actually an instance, which
# has no module at all
if objmodname in self._toloadmods:
# if this is still scheduled for loading, let's proceed immediately,
# but using the object module
self.load_file(self._toloadmods[objmodname], objmodname)
return
# ensure object hasn't been already processed
clsid = '%s.%s' % (modname, objectcls.__name__)
if clsid in self._loadedmods[modname]:
return
self._loadedmods[modname][clsid] = objectcls
# ensure ancestors are registered
for parent in objectcls.__bases__:
self._load_ancestors_then_object(modname, parent, butclasses)
# ensure object is registrable
if objectcls in butclasses or not self.is_registrable(objectcls):
return
# backward compat
reg = self.setdefault(obj_registries(objectcls)[0])
if reg.objname(objectcls)[0] == '_':
warn("[lgc 0.59] object whose name start with '_' won't be "
"skipped anymore at some point, use __abstract__ = True "
"instead (%s)" % objectcls, DeprecationWarning)
return
# register, finally
self.register(objectcls)
@classmethod
def is_registrable(cls, obj):
"""ensure `obj` should be registered
as arbitrary stuff may be registered, do a lot of check and warn about
weird cases (think to dumb proxy objects)
"""
if isinstance(obj, type):
if not issubclass(obj, RegistrableObject):
# ducktyping backward compat
if not (getattr(obj, '__registries__', None)
and getattr(obj, '__regid__', None)
and getattr(obj, '__select__', None)):
return False
elif issubclass(obj, RegistrableInstance):
return False
elif not isinstance(obj, RegistrableInstance):
return False
if not obj.__regid__:
return False # no regid
registries = obj.__registries__
if not registries:
return False # no registries
selector = obj.__select__
if not selector:
return False # no selector
if obj.__dict__.get('__abstract__', False):
return False
# then detect potential problems that should be warned
if not isinstance(registries, (tuple, list)):
cls.warning('%s has __registries__ which is not a list or tuple', obj)
return False
if not callable(selector):
cls.warning('%s has not callable __select__', obj)
return False
return True
# these are overridden by set_log_methods below
# only defining here to prevent pylint from complaining
info = warning = error = critical = exception = debug = lambda msg, *a, **kw: None
# init logging
set_log_methods(RegistryStore, getLogger('registry.store'))
set_log_methods(Registry, getLogger('registry'))
# helpers for debugging selectors
TRACED_OIDS = None
def _trace_selector(cls, selector, args, ret):
vobj = args[0]
if TRACED_OIDS == 'all' or vobj.__regid__ in TRACED_OIDS:
print('%s -> %s for %s(%s)' % (cls, ret, vobj, vobj.__regid__))
def _lltrace(selector):
"""use this decorator on your predicates so they become traceable with
:class:`traced_selection`
"""
def traced(cls, *args, **kwargs):
ret = selector(cls, *args, **kwargs)
if TRACED_OIDS is not None:
_trace_selector(cls, selector, args, ret)
return ret
traced.__name__ = selector.__name__
traced.__doc__ = selector.__doc__
return traced
class traced_selection(object): # pylint: disable=C0103
"""
Typical usage is :
.. sourcecode:: python
>>> from logilab.common.registry import traced_selection
>>> with traced_selection():
... # some code in which you want to debug selectors
... # for all objects
This will yield lines like this in the logs::
selector one_line_rset returned 0 for <class 'elephant.Babar'>
You can also give to :class:`traced_selection` the identifiers of objects on
which you want to debug selection ('oid1' and 'oid2' in the example above).
.. sourcecode:: python
>>> with traced_selection( ('regid1', 'regid2') ):
... # some code in which you want to debug selectors
... # for objects with __regid__ 'regid1' and 'regid2'
A potentially useful point to set up such a tracing function is
the `logilab.common.registry.Registry.select` method body.
"""
def __init__(self, traced='all'):
self.traced = traced
def __enter__(self):
global TRACED_OIDS
TRACED_OIDS = self.traced
def __exit__(self, exctype, exc, traceback):
global TRACED_OIDS
TRACED_OIDS = None
return traceback is None
# selector base classes and operations ########################################
def objectify_predicate(selector_func):
"""Most of the time, a simple score function is enough to build a selector.
The :func:`objectify_predicate` decorator turn it into a proper selector
class::
@objectify_predicate
def one(cls, req, rset=None, **kwargs):
return 1
class MyView(View):
__select__ = View.__select__ & one()
"""
return type(selector_func.__name__, (Predicate,),
{'__doc__': selector_func.__doc__,
'__call__': lambda self, *a, **kw: selector_func(*a, **kw)})
_PREDICATES = {}
def wrap_predicates(decorator):
for predicate in _PREDICATES.values():
if not '_decorators' in predicate.__dict__:
predicate._decorators = set()
if decorator in predicate._decorators:
continue
predicate._decorators.add(decorator)
predicate.__call__ = decorator(predicate.__call__)
class PredicateMetaClass(type):
def __new__(mcs, *args, **kwargs):
# use __new__ so subclasses doesn't have to call Predicate.__init__
inst = type.__new__(mcs, *args, **kwargs)
proxy = weakref.proxy(inst, lambda p: _PREDICATES.pop(id(p)))
_PREDICATES[id(proxy)] = proxy
return inst
@add_metaclass(PredicateMetaClass)
class Predicate(object):
"""base class for selector classes providing implementation
for operators ``&``, ``|`` and ``~``
This class is only here to give access to binary operators, the selector
logic itself should be implemented in the :meth:`__call__` method. Notice it
should usually accept any arbitrary arguments (the context), though that may
vary depending on your usage of the registry.
a selector is called to help choosing the correct object for a
particular context by returning a score (`int`) telling how well
the implementation given as first argument fit to the given context.
0 score means that the class doesn't apply.
"""
@property
def func_name(self):
# backward compatibility
return self.__class__.__name__
def search_selector(self, selector):
"""search for the given selector, selector instance or tuple of
selectors in the selectors tree. Return None if not found.
"""
if self is selector:
return self
if (isinstance(selector, type) or isinstance(selector, tuple)) and \
isinstance(self, selector):
return self
return None
def __str__(self):
return self.__class__.__name__
def __and__(self, other):
return AndPredicate(self, other)
def __rand__(self, other):
return AndPredicate(other, self)
def __iand__(self, other):
return AndPredicate(self, other)
def __or__(self, other):
return OrPredicate(self, other)
def __ror__(self, other):
return OrPredicate(other, self)
def __ior__(self, other):
return OrPredicate(self, other)
def __invert__(self):
return NotPredicate(self)
# XXX (function | function) or (function & function) not managed yet
def __call__(self, cls, *args, **kwargs):
return NotImplementedError("selector %s must implement its logic "
"in its __call__ method" % self.__class__)
def __repr__(self):
return u'<Predicate %s at %x>' % (self.__class__.__name__, id(self))
class MultiPredicate(Predicate):
"""base class for compound selector classes"""
def __init__(self, *selectors):
self.selectors = self.merge_selectors(selectors)
def __str__(self):
return '%s(%s)' % (self.__class__.__name__,
','.join(str(s) for s in self.selectors))
@classmethod
def merge_selectors(cls, selectors):
"""deal with selector instanciation when necessary and merge
multi-selectors if possible:
AndPredicate(AndPredicate(sel1, sel2), AndPredicate(sel3, sel4))
==> AndPredicate(sel1, sel2, sel3, sel4)
"""
merged_selectors = []
for selector in selectors:
# XXX do we really want magic-transformations below?
# if so, wanna warn about them?
if isinstance(selector, types.FunctionType):
selector = objectify_predicate(selector)()
if isinstance(selector, type) and issubclass(selector, Predicate):
selector = selector()
assert isinstance(selector, Predicate), selector
if isinstance(selector, cls):
merged_selectors += selector.selectors
else:
merged_selectors.append(selector)
return merged_selectors
def search_selector(self, selector):
"""search for the given selector or selector instance (or tuple of
selectors) in the selectors tree. Return None if not found
"""
for childselector in self.selectors:
if childselector is selector:
return childselector
found = childselector.search_selector(selector)
if found is not None:
return found
# if not found in children, maybe we are looking for self?
return super(MultiPredicate, self).search_selector(selector)
class AndPredicate(MultiPredicate):
"""and-chained selectors"""
def __call__(self, cls, *args, **kwargs):
score = 0
for selector in self.selectors:
partscore = selector(cls, *args, **kwargs)
if not partscore:
return 0
score += partscore
return score
class OrPredicate(MultiPredicate):
"""or-chained selectors"""
def __call__(self, cls, *args, **kwargs):
for selector in self.selectors:
partscore = selector(cls, *args, **kwargs)
if partscore:
return partscore
return 0
class NotPredicate(Predicate):
"""negation selector"""
def __init__(self, selector):
self.selector = selector
def __call__(self, cls, *args, **kwargs):
score = self.selector(cls, *args, **kwargs)
return int(not score)
def __str__(self):
return 'NOT(%s)' % self.selector
class yes(Predicate): # pylint: disable=C0103
"""Return the score given as parameter, with a default score of 0.5 so any
other selector take precedence.
Usually used for objects which can be selected whatever the context, or
also sometimes to add arbitrary points to a score.
Take care, `yes(0)` could be named 'no'...
"""
def __init__(self, score=0.5):
self.score = score
def __call__(self, *args, **kwargs):
return self.score
# deprecated stuff #############################################################
from logilab.common.deprecation import deprecated
@deprecated('[lgc 0.59] use Registry.objid class method instead')
def classid(cls):
return '%s.%s' % (cls.__module__, cls.__name__)
@deprecated('[lgc 0.59] use obj_registries function instead')
def class_registries(cls, registryname):
return obj_registries(cls, registryname)
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