# encoding: utf-8 """A base class for objects that are configurable.""" # Copyright (c) IPython Development Team. # Distributed under the terms of the Modified BSD License. from __future__ import print_function import logging from copy import deepcopy from .loader import Config, LazyConfigValue from IPython.utils.traitlets import HasTraits, Instance from IPython.utils.text import indent, wrap_paragraphs from IPython.utils.py3compat import iteritems #----------------------------------------------------------------------------- # Helper classes for Configurables #----------------------------------------------------------------------------- class ConfigurableError(Exception): pass class MultipleInstanceError(ConfigurableError): pass #----------------------------------------------------------------------------- # Configurable implementation #----------------------------------------------------------------------------- class Configurable(HasTraits): config = Instance(Config, (), {}) parent = Instance('IPython.config.configurable.Configurable') def __init__(self, **kwargs): """Create a configurable given a config config. Parameters ---------- config : Config If this is empty, default values are used. If config is a :class:`Config` instance, it will be used to configure the instance. parent : Configurable instance, optional The parent Configurable instance of this object. Notes ----- Subclasses of Configurable must call the :meth:`__init__` method of :class:`Configurable` *before* doing anything else and using :func:`super`:: class MyConfigurable(Configurable): def __init__(self, config=None): super(MyConfigurable, self).__init__(config=config) # Then any other code you need to finish initialization. This ensures that instances will be configured properly. """ parent = kwargs.pop('parent', None) if parent is not None: # config is implied from parent if kwargs.get('config', None) is None: kwargs['config'] = parent.config self.parent = parent config = kwargs.pop('config', None) # load kwarg traits, other than config super(Configurable, self).__init__(**kwargs) # load config if config is not None: # We used to deepcopy, but for now we are trying to just save # by reference. This *could* have side effects as all components # will share config. In fact, I did find such a side effect in # _config_changed below. If a config attribute value was a mutable type # all instances of a component were getting the same copy, effectively # making that a class attribute. # self.config = deepcopy(config) self.config = config else: # allow _config_default to return something self._load_config(self.config) # Ensure explicit kwargs are applied after loading config. # This is usually redundant, but ensures config doesn't override # explicitly assigned values. for key, value in kwargs.items(): setattr(self, key, value) #------------------------------------------------------------------------- # Static trait notifiations #------------------------------------------------------------------------- @classmethod def section_names(cls): """return section names as a list""" return [c.__name__ for c in reversed(cls.__mro__) if issubclass(c, Configurable) and issubclass(cls, c) ] def _find_my_config(self, cfg): """extract my config from a global Config object will construct a Config object of only the config values that apply to me based on my mro(), as well as those of my parent(s) if they exist. If I am Bar and my parent is Foo, and their parent is Tim, this will return merge following config sections, in this order:: [Bar, Foo.bar, Tim.Foo.Bar] With the last item being the highest priority. """ cfgs = [cfg] if self.parent: cfgs.append(self.parent._find_my_config(cfg)) my_config = Config() for c in cfgs: for sname in self.section_names(): # Don't do a blind getattr as that would cause the config to # dynamically create the section with name Class.__name__. if c._has_section(sname): my_config.merge(c[sname]) return my_config def _load_config(self, cfg, section_names=None, traits=None): """load traits from a Config object""" if traits is None: traits = self.traits(config=True) if section_names is None: section_names = self.section_names() my_config = self._find_my_config(cfg) # hold trait notifications until after all config has been loaded with self.delay_trait_notifications(): for name, config_value in iteritems(my_config): if name in traits: if isinstance(config_value, LazyConfigValue): # ConfigValue is a wrapper for using append / update on containers # without having to copy the initial value initial = getattr(self, name) config_value = config_value.get_value(initial) # We have to do a deepcopy here if we don't deepcopy the entire # config object. If we don't, a mutable config_value will be # shared by all instances, effectively making it a class attribute. setattr(self, name, deepcopy(config_value)) def _config_changed(self, name, old, new): """Update all the class traits having ``config=True`` as metadata. For any class trait with a ``config`` metadata attribute that is ``True``, we update the trait with the value of the corresponding config entry. """ # Get all traits with a config metadata entry that is True traits = self.traits(config=True) # We auto-load config section for this class as well as any parent # classes that are Configurable subclasses. This starts with Configurable # and works down the mro loading the config for each section. section_names = self.section_names() self._load_config(new, traits=traits, section_names=section_names) def update_config(self, config): """Fire the traits events when the config is updated.""" # Save a copy of the current config. newconfig = deepcopy(self.config) # Merge the new config into the current one. newconfig.merge(config) # Save the combined config as self.config, which triggers the traits # events. self.config = newconfig @classmethod def class_get_help(cls, inst=None): """Get the help string for this class in ReST format. If `inst` is given, it's current trait values will be used in place of class defaults. """ assert inst is None or isinstance(inst, cls) final_help = [] final_help.append(u'%s options' % cls.__name__) final_help.append(len(final_help[0])*u'-') for k, v in sorted(cls.class_traits(config=True).items()): help = cls.class_get_trait_help(v, inst) final_help.append(help) return '\n'.join(final_help) @classmethod def class_get_trait_help(cls, trait, inst=None): """Get the help string for a single trait. If `inst` is given, it's current trait values will be used in place of the class default. """ assert inst is None or isinstance(inst, cls) lines = [] header = "--%s.%s=<%s>" % (cls.__name__, trait.name, trait.__class__.__name__) lines.append(header) if inst is not None: lines.append(indent('Current: %r' % getattr(inst, trait.name), 4)) else: try: dvr = repr(trait.get_default_value()) except Exception: dvr = None # ignore defaults we can't construct if dvr is not None: if len(dvr) > 64: dvr = dvr[:61]+'...' lines.append(indent('Default: %s' % dvr, 4)) if 'Enum' in trait.__class__.__name__: # include Enum choices lines.append(indent('Choices: %r' % (trait.values,))) help = trait.get_metadata('help') if help is not None: help = '\n'.join(wrap_paragraphs(help, 76)) lines.append(indent(help, 4)) return '\n'.join(lines) @classmethod def class_print_help(cls, inst=None): """Get the help string for a single trait and print it.""" print(cls.class_get_help(inst)) @classmethod def class_config_section(cls): """Get the config class config section""" def c(s): """return a commented, wrapped block.""" s = '\n\n'.join(wrap_paragraphs(s, 78)) return '# ' + s.replace('\n', '\n# ') # section header breaker = '#' + '-'*78 s = "# %s configuration" % cls.__name__ lines = [breaker, s, breaker, ''] # get the description trait desc = cls.class_traits().get('description') if desc: desc = desc.default_value else: # no description trait, use __doc__ desc = getattr(cls, '__doc__', '') if desc: lines.append(c(desc)) lines.append('') parents = [] for parent in cls.mro(): # only include parents that are not base classes # and are not the class itself # and have some configurable traits to inherit if parent is not cls and issubclass(parent, Configurable) and \ parent.class_traits(config=True): parents.append(parent) if parents: pstr = ', '.join([ p.__name__ for p in parents ]) lines.append(c('%s will inherit config from: %s'%(cls.__name__, pstr))) lines.append('') for name, trait in iteritems(cls.class_traits(config=True)): help = trait.get_metadata('help') or '' lines.append(c(help)) lines.append('# c.%s.%s = %r'%(cls.__name__, name, trait.get_default_value())) lines.append('') return '\n'.join(lines) class SingletonConfigurable(Configurable): """A configurable that only allows one instance. This class is for classes that should only have one instance of itself or *any* subclass. To create and retrieve such a class use the :meth:`SingletonConfigurable.instance` method. """ _instance = None @classmethod def _walk_mro(cls): """Walk the cls.mro() for parent classes that are also singletons For use in instance() """ for subclass in cls.mro(): if issubclass(cls, subclass) and \ issubclass(subclass, SingletonConfigurable) and \ subclass != SingletonConfigurable: yield subclass @classmethod def clear_instance(cls): """unset _instance for this class and singleton parents. """ if not cls.initialized(): return for subclass in cls._walk_mro(): if isinstance(subclass._instance, cls): # only clear instances that are instances # of the calling class subclass._instance = None @classmethod def instance(cls, *args, **kwargs): """Returns a global instance of this class. This method create a new instance if none have previously been created and returns a previously created instance is one already exists. The arguments and keyword arguments passed to this method are passed on to the :meth:`__init__` method of the class upon instantiation. Examples -------- Create a singleton class using instance, and retrieve it:: >>> from IPython.config.configurable import SingletonConfigurable >>> class Foo(SingletonConfigurable): pass >>> foo = Foo.instance() >>> foo == Foo.instance() True Create a subclass that is retrived using the base class instance:: >>> class Bar(SingletonConfigurable): pass >>> class Bam(Bar): pass >>> bam = Bam.instance() >>> bam == Bar.instance() True """ # Create and save the instance if cls._instance is None: inst = cls(*args, **kwargs) # Now make sure that the instance will also be returned by # parent classes' _instance attribute. for subclass in cls._walk_mro(): subclass._instance = inst if isinstance(cls._instance, cls): return cls._instance else: raise MultipleInstanceError( 'Multiple incompatible subclass instances of ' '%s are being created.' % cls.__name__ ) @classmethod def initialized(cls): """Has an instance been created?""" return hasattr(cls, "_instance") and cls._instance is not None class LoggingConfigurable(Configurable): """A parent class for Configurables that log. Subclasses have a log trait, and the default behavior is to get the logger from the currently running Application. """ log = Instance('logging.Logger') def _log_default(self): from IPython.utils import log return log.get_logger()