Source code for apptools.type_registry.type_registry
# (C) Copyright 2005-2024 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!
[docs]def get_mro(obj_class):
"""Get a reasonable method resolution order of a class and its
superclasses for both old-style and new-style classes.
"""
if not hasattr(obj_class, "__mro__"):
# Old-style class. Mix in object to make a fake new-style class.
try:
obj_class = type(obj_class.__name__, (obj_class, object), {})
except TypeError:
# Old-style extension type that does not descend from object.
mro = [obj_class]
else:
mro = obj_class.__mro__[1:-1]
else:
mro = obj_class.__mro__
return mro
def _mod_name_key(typ):
"""Return a '__module__:__name__' key for a type."""
module = getattr(typ, "__module__", None)
name = getattr(typ, "__name__", None)
key = "{0}:{1}".format(module, name)
return key
[docs]class TypeRegistry(object):
"""Register objects for types.
Each type maintains a stack of registered objects that can be pushed and
popped.
"""
def __init__(self):
# Map types to lists of registered objects. The last is the most
# current and will be the one that is returned on lookup.
self.type_map = {}
# Map '__module__:__name__' strings to lists of registered objects.
self.name_map = {}
# Map abstract base classes to lists of registered objects.
self.abc_map = {}
#### TypeRegistry public interface ########################################
[docs] def push(self, typ, obj):
"""Push an object onto the stack for the given type.
Parameters
----------
typ : type or '__module__:__name__' string for a type
obj : object
The object to register.
"""
if isinstance(typ, str):
# Check the cached types.
for cls in self.type_map:
if _mod_name_key(cls) == typ:
self.type_map[cls].append(obj)
break
else:
if typ not in self.name_map:
self.name_map[typ] = []
self.name_map[typ].append(obj)
else:
if typ not in self.type_map:
self.type_map[typ] = []
self.type_map[typ].append(obj)
[docs] def push_abc(self, typ, obj):
"""Push an object onto the stack for the given ABC.
Parameters
----------
typ : abc.ABCMeta
obj : object
"""
if typ not in self.abc_map:
self.abc_map[typ] = []
self.abc_map[typ].append(obj)
[docs] def pop(self, typ):
"""Pop a registered object for the given type.
Parameters
----------
typ : type or '__module__:__name__' string for a type
Returns
-------
obj : object
The last registered object for the type.
Raises
------
KeyError if the type is not registered.
"""
if isinstance(typ, str):
if typ not in self.name_map:
# We may have it cached in the type map. We will have to
# iterate over all of the types to check.
for cls in self.type_map:
if _mod_name_key(cls) == typ:
old = self._pop_value(self.type_map, cls)
break
else:
raise KeyError("No registered value for {0!r}".format(typ))
else:
old = self._pop_value(self.name_map, typ)
else:
if typ in self.type_map:
old = self._pop_value(self.type_map, typ)
elif typ in self.abc_map:
old = self._pop_value(self.abc_map, typ)
else:
old = self._pop_value(self.name_map, _mod_name_key(typ))
return old
[docs] def lookup(self, instance):
"""Look up the registered object for the given instance.
Parameters
----------
instance : object
An instance of a possibly registered type.
Returns
-------
obj : object
The registered object for the type of the instance, one of the
type's superclasses, or else one of the ABCs the type implements.
Raises
------
KeyError if the instance's type has not been registered.
"""
return self.lookup_by_type(type(instance))
[docs] def lookup_by_type(self, typ):
"""Look up the registered object for a type.
Parameters
----------
typ : type
Returns
-------
obj : object
The registered object for the type, one of its superclasses, or
else one of the ABCs it implements.
Raises
------
KeyError if the type has not been registered.
"""
return self.lookup_all_by_type(typ)[-1]
[docs] def lookup_all(self, instance):
"""Look up all the registered objects for the given instance.
Parameters
----------
instance : object
An instance of a possibly registered type.
Returns
-------
objs : list of objects
The list of registered objects for the instance. If the given
instance is not registered, its superclasses are searched. If none
of the superclasses are registered, search the possible ABCs.
Raises
------
KeyError if the instance's type has not been registered.
"""
return self.lookup_all_by_type(type(instance))
[docs] def lookup_all_by_type(self, typ):
"""Look up all the registered objects for a type.
Parameters
----------
typ : type
Returns
-------
objs : list of objects
The list of registered objects for the type. If the given type is
not registered, its superclasses are searched. If none of the
superclasses are registered, search the possible ABCs.
Raises
------
KeyError if the type has not been registered.
"""
# If a concrete superclass is registered use it.
for cls in get_mro(typ):
if cls in self.type_map or self._in_name_map(cls):
objs = self.type_map[cls]
if objs:
return objs
# None of the concrete superclasses. Check the ABCs.
for abstract, objs in self.abc_map.items():
if issubclass(typ, abstract) and objs:
return objs
# If we have reached here, the lookup failed.
raise KeyError("No registered value for {0!r}".format(typ))
#### Private implementation ###############################################
def _pop_value(self, mapping, key):
"""Pop a value from a keyed stack in a mapping, taking care to remove
the key if the stack is depleted.
"""
objs = mapping[key]
old = objs.pop()
if not objs:
del mapping[key]
return old
def _in_name_map(self, typ):
"""Check if the given type is specified in the name map.
Parameters
----------
typ : type
Returns
-------
is_in_name_map : bool
If True, the registered value will be moved over to the type map
for future lookups.
"""
key = _mod_name_key(typ)
if key in self.name_map:
self.type_map[typ] = self.name_map.pop(key)
return True
else:
return False
[docs]class LazyRegistry(TypeRegistry):
"""A type registry that will lazily import the registered objects.
Register '__module__:__name__' strings for the lazily imported objects.
These will only be imported when the matching type is looked up. The module
name must be a fully-qualified absolute name with all of the parent
packages specified.
"""
[docs] def lookup_by_type(self, typ):
"""Look up the registered object for a type."""
mod_name = TypeRegistry.lookup_by_type(self, typ)
return self._import_object(mod_name)
def _import_object(self, mod_object):
module, name = mod_object.split(":")
mod = __import__(module, {}, {}, [name], 0)
return getattr(mod, name)
