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# util/_preloaded.py
# Copyright (C) 2005-2021 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://www.opensource.org/licenses/mit-license.php
"""supplies the "preloaded" registry to resolve circular module imports at
runtime.
"""
import sys
class _ModuleRegistry:
"""Registry of modules to load in a package init file.
To avoid potential thread safety issues for imports that are deferred
in a function, like https://bugs.python.org/issue38884, these modules
are added to the system module cache by importing them after the packages
has finished initialization.
A global instance is provided under the name :attr:`.preloaded`. Use
the function :func:`.preload_module` to register modules to load and
:meth:`.import_prefix` to load all the modules that start with the
given path.
While the modules are loaded in the global module cache, it's advisable
to access them using :attr:`.preloaded` to ensure that it was actually
registered. Each registered module is added to the instance ``__dict__``
in the form `<package>_<module>`, omitting ``sqlalchemy`` from the package
name. Example: ``sqlalchemy.sql.util`` becomes ``preloaded.sql_util``.
"""
def __init__(self, prefix="sqlalchemy."):
self.module_registry = set()
self.prefix = prefix
def preload_module(self, *deps):
"""Adds the specified modules to the list to load.
This method can be used both as a normal function and as a decorator.
No change is performed to the decorated object.
"""
self.module_registry.update(deps)
return lambda fn: fn
def import_prefix(self, path):
"""Resolve all the modules in the registry that start with the
specified path.
"""
for module in self.module_registry:
if self.prefix:
key = module.split(self.prefix)[-1].replace(".", "_")
else:
key = module
if (
not path or module.startswith(path)
) and key not in self.__dict__:
__import__(module, globals(), locals())
self.__dict__[key] = sys.modules[module]
preloaded = _ModuleRegistry()
preload_module = preloaded.preload_module
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