mirror of
https://github.com/PiBrewing/craftbeerpi4.git
synced 2024-12-13 08:54:55 +01:00
230 lines
7.7 KiB
Python
230 lines
7.7 KiB
Python
"""This module implements a post import hook mechanism styled after what is
|
|
described in PEP-369. Note that it doesn't cope with modules being reloaded.
|
|
|
|
"""
|
|
|
|
import sys
|
|
import threading
|
|
|
|
PY2 = sys.version_info[0] == 2
|
|
|
|
if PY2:
|
|
string_types = basestring,
|
|
else:
|
|
import importlib
|
|
string_types = str,
|
|
|
|
from .decorators import synchronized
|
|
|
|
# The dictionary registering any post import hooks to be triggered once
|
|
# the target module has been imported. Once a module has been imported
|
|
# and the hooks fired, the list of hooks recorded against the target
|
|
# module will be truncacted but the list left in the dictionary. This
|
|
# acts as a flag to indicate that the module had already been imported.
|
|
|
|
_post_import_hooks = {}
|
|
_post_import_hooks_init = False
|
|
_post_import_hooks_lock = threading.RLock()
|
|
|
|
# Register a new post import hook for the target module name. This
|
|
# differs from the PEP-369 implementation in that it also allows the
|
|
# hook function to be specified as a string consisting of the name of
|
|
# the callback in the form 'module:function'. This will result in a
|
|
# proxy callback being registered which will defer loading of the
|
|
# specified module containing the callback function until required.
|
|
|
|
def _create_import_hook_from_string(name):
|
|
def import_hook(module):
|
|
module_name, function = name.split(':')
|
|
attrs = function.split('.')
|
|
__import__(module_name)
|
|
callback = sys.modules[module_name]
|
|
for attr in attrs:
|
|
callback = getattr(callback, attr)
|
|
return callback(module)
|
|
return import_hook
|
|
|
|
@synchronized(_post_import_hooks_lock)
|
|
def register_post_import_hook(hook, name):
|
|
# Create a deferred import hook if hook is a string name rather than
|
|
# a callable function.
|
|
|
|
if isinstance(hook, string_types):
|
|
hook = _create_import_hook_from_string(hook)
|
|
|
|
# Automatically install the import hook finder if it has not already
|
|
# been installed.
|
|
|
|
global _post_import_hooks_init
|
|
|
|
if not _post_import_hooks_init:
|
|
_post_import_hooks_init = True
|
|
sys.meta_path.insert(0, ImportHookFinder())
|
|
|
|
# Determine if any prior registration of a post import hook for
|
|
# the target modules has occurred and act appropriately.
|
|
|
|
hooks = _post_import_hooks.get(name, None)
|
|
|
|
if hooks is None:
|
|
# No prior registration of post import hooks for the target
|
|
# module. We need to check whether the module has already been
|
|
# imported. If it has we fire the hook immediately and add an
|
|
# empty list to the registry to indicate that the module has
|
|
# already been imported and hooks have fired. Otherwise add
|
|
# the post import hook to the registry.
|
|
|
|
module = sys.modules.get(name, None)
|
|
|
|
if module is not None:
|
|
_post_import_hooks[name] = []
|
|
hook(module)
|
|
|
|
else:
|
|
_post_import_hooks[name] = [hook]
|
|
|
|
elif hooks == []:
|
|
# A prior registration of port import hooks for the target
|
|
# module was done and the hooks already fired. Fire the hook
|
|
# immediately.
|
|
|
|
module = sys.modules[name]
|
|
hook(module)
|
|
|
|
else:
|
|
# A prior registration of port import hooks for the target
|
|
# module was done but the module has not yet been imported.
|
|
|
|
_post_import_hooks[name].append(hook)
|
|
|
|
# Register post import hooks defined as package entry points.
|
|
|
|
def _create_import_hook_from_entrypoint(entrypoint):
|
|
def import_hook(module):
|
|
__import__(entrypoint.module_name)
|
|
callback = sys.modules[entrypoint.module_name]
|
|
for attr in entrypoint.attrs:
|
|
callback = getattr(callback, attr)
|
|
return callback(module)
|
|
return import_hook
|
|
|
|
def discover_post_import_hooks(group):
|
|
try:
|
|
import pkg_resources
|
|
except ImportError:
|
|
return
|
|
|
|
for entrypoint in pkg_resources.iter_entry_points(group=group):
|
|
callback = _create_import_hook_from_entrypoint(entrypoint)
|
|
register_post_import_hook(callback, entrypoint.name)
|
|
|
|
# Indicate that a module has been loaded. Any post import hooks which
|
|
# were registered against the target module will be invoked. If an
|
|
# exception is raised in any of the post import hooks, that will cause
|
|
# the import of the target module to fail.
|
|
|
|
@synchronized(_post_import_hooks_lock)
|
|
def notify_module_loaded(module):
|
|
name = getattr(module, '__name__', None)
|
|
hooks = _post_import_hooks.get(name, None)
|
|
|
|
if hooks:
|
|
_post_import_hooks[name] = []
|
|
|
|
for hook in hooks:
|
|
hook(module)
|
|
|
|
# A custom module import finder. This intercepts attempts to import
|
|
# modules and watches out for attempts to import target modules of
|
|
# interest. When a module of interest is imported, then any post import
|
|
# hooks which are registered will be invoked.
|
|
|
|
class _ImportHookLoader:
|
|
|
|
def load_module(self, fullname):
|
|
module = sys.modules[fullname]
|
|
notify_module_loaded(module)
|
|
|
|
return module
|
|
|
|
class _ImportHookChainedLoader:
|
|
|
|
def __init__(self, loader):
|
|
self.loader = loader
|
|
|
|
def load_module(self, fullname):
|
|
module = self.loader.load_module(fullname)
|
|
notify_module_loaded(module)
|
|
|
|
return module
|
|
|
|
class ImportHookFinder:
|
|
|
|
def __init__(self):
|
|
self.in_progress = {}
|
|
|
|
@synchronized(_post_import_hooks_lock)
|
|
def find_module(self, fullname, path=None):
|
|
# If the module being imported is not one we have registered
|
|
# post import hooks for, we can return immediately. We will
|
|
# take no further part in the importing of this module.
|
|
|
|
if not fullname in _post_import_hooks:
|
|
return None
|
|
|
|
# When we are interested in a specific module, we will call back
|
|
# into the import system a second time to defer to the import
|
|
# finder that is supposed to handle the importing of the module.
|
|
# We set an in progress flag for the target module so that on
|
|
# the second time through we don't trigger another call back
|
|
# into the import system and cause a infinite loop.
|
|
|
|
if fullname in self.in_progress:
|
|
return None
|
|
|
|
self.in_progress[fullname] = True
|
|
|
|
# Now call back into the import system again.
|
|
|
|
try:
|
|
if PY2:
|
|
# For Python 2 we don't have much choice but to
|
|
# call back in to __import__(). This will
|
|
# actually cause the module to be imported. If no
|
|
# module could be found then ImportError will be
|
|
# raised. Otherwise we return a loader which
|
|
# returns the already loaded module and invokes
|
|
# the post import hooks.
|
|
|
|
__import__(fullname)
|
|
|
|
return _ImportHookLoader()
|
|
|
|
else:
|
|
# For Python 3 we need to use find_spec().loader
|
|
# from the importlib.util module. It doesn't actually
|
|
# import the target module and only finds the
|
|
# loader. If a loader is found, we need to return
|
|
# our own loader which will then in turn call the
|
|
# real loader to import the module and invoke the
|
|
# post import hooks.
|
|
try:
|
|
import importlib.util
|
|
loader = importlib.util.find_spec(fullname).loader
|
|
except (ImportError, AttributeError):
|
|
loader = importlib.find_loader(fullname, path)
|
|
if loader:
|
|
return _ImportHookChainedLoader(loader)
|
|
|
|
|
|
finally:
|
|
del self.in_progress[fullname]
|
|
|
|
# Decorator for marking that a function should be called as a post
|
|
# import hook when the target module is imported.
|
|
|
|
def when_imported(name):
|
|
def register(hook):
|
|
register_post_import_hook(hook, name)
|
|
return hook
|
|
return register
|