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"""Class Namespaces (internal module). |
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All of the guts of the class namespace implementation. |
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""" |
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# See https://blog.ionelmc.ro/2015/02/09/understanding-python-metaclasses/ |
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import collections.abc |
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import functools |
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import itertools |
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import weakref |
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from .descriptor_inspector import _DescriptorInspector |
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from .flags import ENABLE_SET_NAME |
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from .proxy import _Proxy |
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_PROXY_INFOS = weakref.WeakKeyDictionary() |
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def _mro_to_chained(mro, dct): |
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"""Return a chained map of lookups for the given namespace and mro.""" |
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return collections.ChainMap(*[ |
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Namespace.get_namespace(cls, dct.path) for cls in |
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itertools.takewhile( |
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functools.partial(Namespace.no_blocker, dct), |
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(cls for cls in mro if isinstance(cls, Namespaceable))) if |
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Namespace.namespace_exists(dct.path, cls)]) |
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def _instance_map(ns_proxy): |
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"""Return a map, possibly chained, of lookups for the given instance.""" |
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dct, instance, _ = _PROXY_INFOS[ns_proxy] |
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if instance is not None: |
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if isinstance(instance, Namespaceable): |
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return _mro_to_chained(instance.__mro__, dct) |
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else: |
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return Namespace.get_namespace(instance, dct.path) |
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else: |
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return {} |
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def _mro_map(ns_proxy): |
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"""Return a chained map of lookups for the given owner class.""" |
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dct, _, owner = _PROXY_INFOS[ns_proxy] |
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mro = owner.__mro__ |
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mro = mro[mro.index(dct.parent_object):] |
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return _mro_to_chained(mro, dct) |
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def _retarget(ns_proxy): |
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"""Convert a class lookup to an instance lookup, if needed.""" |
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dct, instance, owner = _PROXY_INFOS[ns_proxy] |
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if instance is None and isinstance(type(owner), Namespaceable): |
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instance, owner = owner, type(owner) |
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dct = Namespace.get_namespace(owner, dct.path) |
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ns_proxy = _NamespaceProxy(dct, instance, owner) |
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return ns_proxy |
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def _get(a_map, name): |
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"""Return a _DescriptorInspector around the attribute, or None.""" |
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try: |
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value = a_map[name] |
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except KeyError: |
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return None |
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else: |
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return _DescriptorInspector(value) |
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def _delete(dct, name): |
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"""Attempt to delete `name` from `dct`. Raise AttributeError if missing.""" |
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try: |
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del dct[name] |
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except KeyError: |
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raise AttributeError(name) |
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def _has_get(value): |
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"""Return whether the value is a wrapped getter descriptor.""" |
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return value is not None and value.has_get |
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def _is_data(value): |
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"""Return whether the value is a wrapped data descriptor.""" |
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return value is not None and value.is_data |
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def _get_data(dct, name): |
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"""Return the data descriptor associated with `name` in `dct`, if any.""" |
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value = _get(dct, name) |
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if _is_data(value): |
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return value |
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class _NamespaceProxy(_Proxy): |
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"""Proxy object for manipulating and querying namespaces.""" |
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__slots__ = '__weakref__', |
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def __init__(self, dct, instance, owner): |
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_PROXY_INFOS[self] = dct, instance, owner |
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def __dir__(self): |
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return collections.ChainMap(_instance_map(self), _mro_map(self)) |
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def __getattribute__(self, name): |
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self = _retarget(self) |
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_, instance, owner = _PROXY_INFOS[self] |
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instance_map = _instance_map(self) |
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mro_map = _mro_map(self) |
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instance_value = _get(instance_map, name) |
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mro_value = _get(mro_map, name) |
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if _is_data(mro_value): |
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return mro_value.get(instance, owner) |
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elif issubclass(owner, type) and _has_get(instance_value): |
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return instance_value.get(None, instance) |
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elif instance_value is not None: |
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return instance_value.object |
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elif _has_get(mro_value): |
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return mro_value.get(instance, owner) |
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elif mro_value is not None: |
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return mro_value.object |
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else: |
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raise AttributeError(name) |
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def __setattr__(self, name, value): |
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self = _retarget(self) |
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dct, instance, owner = _PROXY_INFOS[self] |
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if instance is None: |
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real_map = Namespace.get_namespace(owner, dct.path) |
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real_map[name] = value |
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return |
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mro_map = _mro_map(self) |
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target_value = _get_data(mro_map, name) |
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if target_value is not None: |
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target_value.set(instance, value) |
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return |
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instance_map = Namespace.get_namespace(instance, dct.path) |
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instance_map[name] = value |
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def __delattr__(self, name): |
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self = _retarget(self) |
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dct, instance, owner = _PROXY_INFOS[self] |
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real_map = Namespace.get_namespace(owner, dct.path) |
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if instance is None: |
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_delete(real_map, name) |
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return |
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value = _get_data(real_map, name) |
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if value is not None: |
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value.delete(instance) |
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return |
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instance_map = Namespace.get_namespace(instance, dct.path) |
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_delete(instance_map, name) |
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class _ScopeProxy(_Proxy): |
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"""Proxy object for manipulating namespaces during class creation.""" |
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__slots__ = '__weakref__', |
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def __init__(self, dct): |
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_PROXY_INFOS[self] = dct |
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def __dir__(self): |
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return _PROXY_INFOS[self] |
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def __getattribute__(self, name): |
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dct = _PROXY_INFOS[self] |
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try: |
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return dct[name] |
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except KeyError: |
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raise AttributeError(name) |
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def __setattr__(self, name, value): |
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_PROXY_INFOS[self][name] = value |
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def __delattr__(self, name): |
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_delete(_PROXY_INFOS[self], name) |
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def __enter__(self): |
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return _PROXY_INFOS[self].__enter__() |
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def __exit__(self, exc_type, exc_value, traceback): |
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return _PROXY_INFOS[self].__exit__(exc_type, exc_value, traceback) |
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class Namespace(dict): |
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"""Namespace.""" |
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__slots__ = 'name', 'scope', 'parent', 'active', 'parent_object' |
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__namespaces = {} |
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def __init__(self, *args, **kwargs): |
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super().__init__(*args, **kwargs) |
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bad_values = tuple( |
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value for value in self.values() if |
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isinstance(value, (Namespace, _Proxy))) |
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if bad_values: |
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raise ValueError('Bad values: {}'.format(bad_values)) |
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self.name = None |
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self.scope = None |
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self.parent = None |
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self.active = False |
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self.parent_object = None |
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@classmethod |
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def premake(cls, name, parent): |
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"""Return an empty namespace with the given name and parent.""" |
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self = cls() |
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self.name = name |
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self.parent = parent |
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return self |
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def __setitem__(self, key, value): |
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if ( |
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self.parent_object is not None and |
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isinstance(value, Namespace) and value.name != key): |
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value.push(key, self.scope) |
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value.add(self.parent_object) |
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super().__setitem__(key, value) |
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def __enter__(self): |
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self.activate() |
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return self |
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def __exit__(self, exc_type, exc_value, traceback): |
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if self.name is None: |
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raise RuntimeError('Namespace must be named.') |
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self.deactivate() |
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@property |
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def path(self): |
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"""Return the full path of the namespace.""" |
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if self.name is None or self.parent is None: |
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raise ValueError |
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if isinstance(self.parent, Namespace): |
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parent_path = self.parent.path |
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else: |
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parent_path = () |
247
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return parent_path + (self.name,) |
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249
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@classmethod |
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def __get_helper(cls, target, path): |
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"""Return the namespace for `target` at `path`, create if needed.""" |
252
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if isinstance(target, Namespaceable): |
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path_ = target, path |
254
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namespaces = cls.__namespaces |
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else: |
256
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path_ = path |
257
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try: |
258
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namespaces = target.__namespaces |
259
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except AttributeError: |
260
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namespaces = {} |
261
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target.__namespaces = namespaces |
262
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return path_, namespaces |
263
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264
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@classmethod |
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def namespace_exists(cls, path, target): |
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"""Return whether the given namespace exists.""" |
267
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path_, namespaces = cls.__get_helper(target, path) |
268
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return path_ in namespaces |
269
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270
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@classmethod |
271
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def get_namespace(cls, target, path): |
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"""Return a namespace with given target and path, create if needed.""" |
273
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path_, namespaces = cls.__get_helper(target, path) |
274
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try: |
275
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return namespaces[path_] |
276
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except KeyError: |
277
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if len(path) == 1: |
278
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parent = {} |
279
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else: |
280
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parent = cls.get_namespace(target, path[:-1]) |
281
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return namespaces.setdefault(path_, cls.premake(path[-1], parent)) |
282
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283
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6 |
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@classmethod |
284
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def no_blocker(cls, dct, cls_): |
285
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"""Return False if there's a non-Namespace object in the path.""" |
286
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6 |
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try: |
287
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6 |
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namespace = vars(cls_) |
288
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6 |
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for name in dct.path: |
289
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6 |
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namespace = namespace[name] |
290
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6 |
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if not isinstance(namespace, cls): |
291
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return False |
292
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6 |
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except KeyError: |
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293
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pass |
294
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6 |
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return True |
295
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296
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6 |
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def add(self, target): |
297
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"""Add self as a namespace under target.""" |
298
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6 |
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path, namespaces = self.__get_helper(target, self.path) |
299
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6 |
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res = namespaces.setdefault(path, self) |
300
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6 |
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if res is self: |
301
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6 |
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self.parent_object = target |
302
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303
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6 |
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def set_if_none(self, name, value): |
304
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"""Set the attribute `name` to `value`, if it's initially None.""" |
305
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6 |
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if getattr(self, name) is None: |
306
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6 |
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setattr(self, name, value) |
307
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|
308
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6 |
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def push(self, name, scope): |
309
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"""Bind self to the given name and scope, and activate.""" |
310
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6 |
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self.set_if_none('name', name) |
311
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6 |
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self.set_if_none('scope', scope) |
312
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6 |
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self.set_if_none('parent', scope.dicts[0]) |
313
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6 |
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if name != self.name: |
314
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6 |
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raise ValueError('Cannot rename namespace') |
315
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6 |
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if scope is not self.scope: |
316
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raise ValueError('Cannot reuse namespace') |
317
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6 |
|
if scope.dicts[0] is not self.parent: |
318
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raise ValueError('Cannot reparent namespace') |
319
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6 |
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self.scope.namespaces.append(self) |
320
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6 |
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self.activate() |
321
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|
322
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6 |
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def activate(self): |
323
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"""Take over as the scope for the target.""" |
324
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6 |
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if self.scope is not None and not self.active: |
325
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6 |
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if self.scope.dicts[0] is not self.parent: |
326
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raise ValueError('Cannot reparent namespace') |
327
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6 |
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self.active = True |
328
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6 |
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self.scope.dicts.insert(0, self) |
329
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|
330
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6 |
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def deactivate(self): |
331
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"""Stop being the scope for the target.""" |
332
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6 |
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if self.scope is not None and self.active: |
333
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6 |
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self.active = False |
334
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6 |
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self.scope.dicts.pop(0) |
335
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|
336
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6 |
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def __get__(self, instance, owner): |
337
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6 |
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return _NamespaceProxy(self, instance, owner) |
338
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|
339
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|
340
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6 |
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class _NamespaceScope(collections.abc.MutableMapping): |
341
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|
342
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"""The class creation namespace for Namespaceables.""" |
343
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|
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|
344
|
6 |
|
__slots__ = 'dicts', 'namespaces' |
345
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|
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|
346
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6 |
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def __init__(self, dct): |
347
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6 |
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self.dicts = [dct] |
348
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6 |
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self.namespaces = [] |
349
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|
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|
350
|
6 |
|
def __getitem__(self, key): |
351
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6 |
|
value = collections.ChainMap(*self.dicts)[key] |
352
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6 |
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if isinstance(value, Namespace): |
353
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6 |
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value = _ScopeProxy(value) |
354
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6 |
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return value |
355
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356
|
6 |
|
def __setitem__(self, key, value): |
357
|
6 |
|
dct = self.dicts[0] |
358
|
6 |
|
if isinstance(value, _ScopeProxy): |
359
|
6 |
|
value = _PROXY_INFOS[value] |
360
|
6 |
|
if isinstance(value, Namespace) and value.name != key: |
361
|
6 |
|
value.push(key, self) |
362
|
6 |
|
dct[key] = value |
363
|
|
|
|
364
|
6 |
|
def __delitem__(self, key): |
365
|
6 |
|
del self.dicts[0][key] |
366
|
|
|
|
367
|
6 |
|
def __iter__(self): |
368
|
|
|
return iter(collections.ChainMap(*self.dicts)) |
369
|
|
|
|
370
|
6 |
|
def __len__(self): |
371
|
|
|
return len(collections.ChainMap(*self.dicts)) |
372
|
|
|
|
373
|
|
|
|
374
|
6 |
|
_NAMESPACE_SCOPES = weakref.WeakKeyDictionary() |
375
|
|
|
|
376
|
|
|
|
377
|
6 |
|
class Namespaceable(type): |
378
|
|
|
|
379
|
|
|
"""Metaclass for classes that can contain namespaces.""" |
380
|
|
|
|
381
|
6 |
|
@classmethod |
382
|
|
|
def __prepare__(mcs, name, bases, **kwargs): |
383
|
6 |
|
return _NamespaceScope(super().__prepare__(name, bases, **kwargs)) |
384
|
|
|
|
385
|
6 |
|
def __new__(mcs, name, bases, dct, **kwargs): |
386
|
6 |
|
cls = super().__new__(mcs, name, bases, dct.dicts[0], **kwargs) |
387
|
6 |
|
_NAMESPACE_SCOPES[cls] = dct |
388
|
6 |
|
for namespace in dct.namespaces: |
389
|
6 |
|
namespace.add(cls) |
390
|
6 |
|
if ENABLE_SET_NAME: |
391
|
2 |
|
for name, value in namespace.items(): |
392
|
2 |
|
wrapped = _DescriptorInspector(value) |
393
|
2 |
|
if wrapped.has_set_name: |
394
|
2 |
|
wrapped.set_name(cls, name) |
395
|
6 |
|
return cls |
396
|
|
|
|
397
|
6 |
|
def __setattr__(cls, name, value): |
398
|
6 |
|
if isinstance(value, Namespace) and value.name != name: |
399
|
6 |
|
value.push(name, _NAMESPACE_SCOPES[cls]) |
400
|
6 |
|
value.add(cls) |
401
|
6 |
|
if issubclass(cls, Namespaceable): |
402
|
6 |
|
super().__setattr__(cls, name, value) |
403
|
|
|
else: |
404
|
|
|
super().__setattr__(name, value) |
405
|
|
|
|
Except handlers which only contain
pass
and do not have anelse
clause can usually simply be removed: