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69 lines
2.3 KiB
69 lines
2.3 KiB
# util/_preloaded.py
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# Copyright (C) 2005-2022 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: https://www.opensource.org/licenses/mit-license.php
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"""supplies the "preloaded" registry to resolve circular module imports at
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runtime.
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"""
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import sys
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from . import compat
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class _ModuleRegistry:
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"""Registry of modules to load in a package init file.
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To avoid potential thread safety issues for imports that are deferred
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in a function, like https://bugs.python.org/issue38884, these modules
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are added to the system module cache by importing them after the packages
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has finished initialization.
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A global instance is provided under the name :attr:`.preloaded`. Use
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the function :func:`.preload_module` to register modules to load and
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:meth:`.import_prefix` to load all the modules that start with the
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given path.
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While the modules are loaded in the global module cache, it's advisable
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to access them using :attr:`.preloaded` to ensure that it was actually
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registered. Each registered module is added to the instance ``__dict__``
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in the form `<package>_<module>`, omitting ``sqlalchemy`` from the package
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name. Example: ``sqlalchemy.sql.util`` becomes ``preloaded.sql_util``.
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"""
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def __init__(self, prefix="sqlalchemy."):
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self.module_registry = set()
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self.prefix = prefix
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def preload_module(self, *deps):
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"""Adds the specified modules to the list to load.
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This method can be used both as a normal function and as a decorator.
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No change is performed to the decorated object.
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"""
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self.module_registry.update(deps)
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return lambda fn: fn
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def import_prefix(self, path):
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"""Resolve all the modules in the registry that start with the
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specified path.
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"""
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for module in self.module_registry:
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if self.prefix:
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key = module.split(self.prefix)[-1].replace(".", "_")
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else:
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key = module
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if (
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not path or module.startswith(path)
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) and key not in self.__dict__:
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compat.import_(module, globals(), locals())
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self.__dict__[key] = sys.modules[module]
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preloaded = _ModuleRegistry()
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preload_module = preloaded.preload_module
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