"""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, _BACKCOMPAT_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('{!r} is not a relative name '

'(no leading dot)'.format(name))

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 _Module(types.ModuleType):

"""A subclass of the module type to allow __class__ manipulation."""

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__ = _Module

# 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

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]):

msg = ('module object for {!r} substituted in sys.modules '

'during a lazy load')

raise ValueError(msg.format(original_name))

# 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):

"""Create a module which can have its __class__ manipulated."""

return _Module(spec.name)

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__.

module.__spec__.loader_state = module.__dict__.copy()

module.__class__ = _LazyModule