295 lines
11 KiB
Python
295 lines
11 KiB
Python
"""Utility code for constructing importers, etc."""
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from . import abc
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from ._bootstrap import module_from_spec
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from ._bootstrap import _resolve_name
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from ._bootstrap import spec_from_loader
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from ._bootstrap import _find_spec
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from ._bootstrap_external import MAGIC_NUMBER
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from ._bootstrap_external import cache_from_source
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from ._bootstrap_external import decode_source
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from ._bootstrap_external import source_from_cache
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from ._bootstrap_external import spec_from_file_location
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from contextlib import contextmanager
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import functools
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import sys
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import types
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import warnings
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def resolve_name(name, package):
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"""Resolve a relative module name to an absolute one."""
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if not name.startswith('.'):
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return name
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elif not package:
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raise ValueError('{!r} is not a relative name '
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'(no leading dot)'.format(name))
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level = 0
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for character in name:
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if character != '.':
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break
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level += 1
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return _resolve_name(name[level:], package, level)
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def _find_spec_from_path(name, path=None):
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"""Return the spec for the specified module.
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First, sys.modules is checked to see if the module was already imported. If
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so, then sys.modules[name].__spec__ is returned. If that happens to be
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set to None, then ValueError is raised. If the module is not in
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sys.modules, then sys.meta_path is searched for a suitable spec with the
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value of 'path' given to the finders. None is returned if no spec could
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be found.
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Dotted names do not have their parent packages implicitly imported. You will
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most likely need to explicitly import all parent packages in the proper
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order for a submodule to get the correct spec.
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"""
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if name not in sys.modules:
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return _find_spec(name, path)
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else:
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module = sys.modules[name]
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if module is None:
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return None
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try:
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spec = module.__spec__
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except AttributeError:
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raise ValueError('{}.__spec__ is not set'.format(name)) from None
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else:
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if spec is None:
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raise ValueError('{}.__spec__ is None'.format(name))
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return spec
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def find_spec(name, package=None):
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"""Return the spec for the specified module.
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First, sys.modules is checked to see if the module was already imported. If
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so, then sys.modules[name].__spec__ is returned. If that happens to be
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set to None, then ValueError is raised. If the module is not in
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sys.modules, then sys.meta_path is searched for a suitable spec with the
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value of 'path' given to the finders. None is returned if no spec could
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be found.
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If the name is for submodule (contains a dot), the parent module is
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automatically imported.
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The name and package arguments work the same as importlib.import_module().
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In other words, relative module names (with leading dots) work.
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"""
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fullname = resolve_name(name, package) if name.startswith('.') else name
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if fullname not in sys.modules:
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parent_name = fullname.rpartition('.')[0]
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if parent_name:
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# Use builtins.__import__() in case someone replaced it.
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parent = __import__(parent_name, fromlist=['__path__'])
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return _find_spec(fullname, parent.__path__)
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else:
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return _find_spec(fullname, None)
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else:
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module = sys.modules[fullname]
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if module is None:
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return None
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try:
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spec = module.__spec__
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except AttributeError:
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raise ValueError('{}.__spec__ is not set'.format(name)) from None
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else:
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if spec is None:
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raise ValueError('{}.__spec__ is None'.format(name))
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return spec
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@contextmanager
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def _module_to_load(name):
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is_reload = name in sys.modules
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module = sys.modules.get(name)
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if not is_reload:
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# This must be done before open() is called as the 'io' module
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# implicitly imports 'locale' and would otherwise trigger an
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# infinite loop.
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module = type(sys)(name)
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# This must be done before putting the module in sys.modules
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# (otherwise an optimization shortcut in import.c becomes wrong)
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module.__initializing__ = True
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sys.modules[name] = module
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try:
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yield module
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except Exception:
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if not is_reload:
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try:
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del sys.modules[name]
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except KeyError:
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pass
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finally:
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module.__initializing__ = False
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def set_package(fxn):
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"""Set __package__ on the returned module.
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This function is deprecated.
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"""
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@functools.wraps(fxn)
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def set_package_wrapper(*args, **kwargs):
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warnings.warn('The import system now takes care of this automatically.',
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DeprecationWarning, stacklevel=2)
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module = fxn(*args, **kwargs)
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if getattr(module, '__package__', None) is None:
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module.__package__ = module.__name__
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if not hasattr(module, '__path__'):
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module.__package__ = module.__package__.rpartition('.')[0]
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return module
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return set_package_wrapper
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def set_loader(fxn):
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"""Set __loader__ on the returned module.
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This function is deprecated.
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"""
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@functools.wraps(fxn)
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def set_loader_wrapper(self, *args, **kwargs):
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warnings.warn('The import system now takes care of this automatically.',
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DeprecationWarning, stacklevel=2)
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module = fxn(self, *args, **kwargs)
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if getattr(module, '__loader__', None) is None:
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module.__loader__ = self
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return module
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return set_loader_wrapper
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def module_for_loader(fxn):
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"""Decorator to handle selecting the proper module for loaders.
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The decorated function is passed the module to use instead of the module
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name. The module passed in to the function is either from sys.modules if
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it already exists or is a new module. If the module is new, then __name__
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is set the first argument to the method, __loader__ is set to self, and
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__package__ is set accordingly (if self.is_package() is defined) will be set
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before it is passed to the decorated function (if self.is_package() does
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not work for the module it will be set post-load).
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If an exception is raised and the decorator created the module it is
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subsequently removed from sys.modules.
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The decorator assumes that the decorated function takes the module name as
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the second argument.
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"""
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warnings.warn('The import system now takes care of this automatically.',
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DeprecationWarning, stacklevel=2)
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@functools.wraps(fxn)
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def module_for_loader_wrapper(self, fullname, *args, **kwargs):
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with _module_to_load(fullname) as module:
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module.__loader__ = self
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try:
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is_package = self.is_package(fullname)
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except (ImportError, AttributeError):
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pass
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else:
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if is_package:
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module.__package__ = fullname
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else:
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module.__package__ = fullname.rpartition('.')[0]
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# If __package__ was not set above, __import__() will do it later.
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return fxn(self, module, *args, **kwargs)
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return module_for_loader_wrapper
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class _Module(types.ModuleType):
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"""A subclass of the module type to allow __class__ manipulation."""
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class _LazyModule(types.ModuleType):
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"""A subclass of the module type which triggers loading upon attribute access."""
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def __getattribute__(self, attr):
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"""Trigger the load of the module and return the attribute."""
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# All module metadata must be garnered from __spec__ in order to avoid
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# using mutated values.
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# Stop triggering this method.
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self.__class__ = _Module
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# Get the original name to make sure no object substitution occurred
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# in sys.modules.
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original_name = self.__spec__.name
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# Figure out exactly what attributes were mutated between the creation
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# of the module and now.
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attrs_then = self.__spec__.loader_state
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attrs_now = self.__dict__
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attrs_updated = {}
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for key, value in attrs_now.items():
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# Code that set the attribute may have kept a reference to the
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# assigned object, making identity more important than equality.
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if key not in attrs_then:
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attrs_updated[key] = value
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elif id(attrs_now[key]) != id(attrs_then[key]):
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attrs_updated[key] = value
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self.__spec__.loader.exec_module(self)
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# If exec_module() was used directly there is no guarantee the module
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# object was put into sys.modules.
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if original_name in sys.modules:
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if id(self) != id(sys.modules[original_name]):
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msg = ('module object for {!r} substituted in sys.modules '
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'during a lazy load')
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raise ValueError(msg.format(original_name))
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# Update after loading since that's what would happen in an eager
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# loading situation.
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self.__dict__.update(attrs_updated)
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return getattr(self, attr)
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def __delattr__(self, attr):
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"""Trigger the load and then perform the deletion."""
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# To trigger the load and raise an exception if the attribute
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# doesn't exist.
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self.__getattribute__(attr)
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delattr(self, attr)
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class LazyLoader(abc.Loader):
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"""A loader that creates a module which defers loading until attribute access."""
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@staticmethod
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def __check_eager_loader(loader):
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if not hasattr(loader, 'exec_module'):
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raise TypeError('loader must define exec_module()')
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elif hasattr(loader.__class__, 'create_module'):
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if abc.Loader.create_module != loader.__class__.create_module:
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# Only care if create_module() is overridden in a subclass of
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# importlib.abc.Loader.
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raise TypeError('loader cannot define create_module()')
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@classmethod
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def factory(cls, loader):
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"""Construct a callable which returns the eager loader made lazy."""
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cls.__check_eager_loader(loader)
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return lambda *args, **kwargs: cls(loader(*args, **kwargs))
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def __init__(self, loader):
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self.__check_eager_loader(loader)
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self.loader = loader
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def create_module(self, spec):
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"""Create a module which can have its __class__ manipulated."""
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return _Module(spec.name)
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def exec_module(self, module):
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"""Make the module load lazily."""
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module.__spec__.loader = self.loader
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module.__loader__ = self.loader
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# Don't need to worry about deep-copying as trying to set an attribute
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# on an object would have triggered the load,
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# e.g. ``module.__spec__.loader = None`` would trigger a load from
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# trying to access module.__spec__.
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module.__spec__.loader_state = module.__dict__.copy()
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module.__class__ = _LazyModule
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