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