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# demandimportpy3 - global demand-loading of modules for Mercurial
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#
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# Copyright 2017 Facebook Inc.
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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"""Lazy loading for Python 3.6 and above.
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This uses the new importlib finder/loader functionality available in Python 3.5
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and up. The code reuses most of the mechanics implemented inside importlib.util,
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but with a few additions:
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* Allow excluding certain modules from lazy imports.
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* Expose an interface that's substantially the same as demandimport for
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Python 2.
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This also has some limitations compared to the Python 2 implementation:
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* Much of the logic is per-package, not per-module, so any packages loaded
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before demandimport is enabled will not be lazily imported in the future. In
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practice, we only expect builtins to be loaded before demandimport is
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enabled.
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"""
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# This line is unnecessary, but it satisfies test-check-py3-compat.t.
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from __future__ import absolute_import
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import contextlib
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import importlib.abc
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import importlib.machinery
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import importlib.util
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import sys
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_deactivated = False
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class _lazyloaderex(importlib.util.LazyLoader):
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"""This is a LazyLoader except it also follows the _deactivated global and
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the ignore list.
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"""
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def exec_module(self, module):
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"""Make the module load lazily."""
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if _deactivated or module.__name__ in ignore:
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self.loader.exec_module(module)
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else:
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super().exec_module(module)
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# This is 3.6+ because with Python 3.5 it isn't possible to lazily load
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# extensions. See the discussion in https://python.org/sf/26186 for more.
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_extensions_loader = _lazyloaderex.factory(
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importlib.machinery.ExtensionFileLoader)
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_bytecode_loader = _lazyloaderex.factory(
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importlib.machinery.SourcelessFileLoader)
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_source_loader = _lazyloaderex.factory(importlib.machinery.SourceFileLoader)
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def _makefinder(path):
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return importlib.machinery.FileFinder(
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path,
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# This is the order in which loaders are passed in in core Python.
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(_extensions_loader, importlib.machinery.EXTENSION_SUFFIXES),
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(_source_loader, importlib.machinery.SOURCE_SUFFIXES),
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(_bytecode_loader, importlib.machinery.BYTECODE_SUFFIXES),
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)
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ignore = []
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def init(ignorelist):
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global ignore
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ignore = ignorelist
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def isenabled():
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return _makefinder in sys.path_hooks and not _deactivated
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def disable():
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try:
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while True:
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sys.path_hooks.remove(_makefinder)
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except ValueError:
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pass
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def enable():
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sys.path_hooks.insert(0, _makefinder)
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@contextlib.contextmanager
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def deactivated():
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# This implementation is a bit different from Python 2's. Python 3
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# maintains a per-package finder cache in sys.path_importer_cache (see
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# PEP 302). This means that we can't just call disable + enable.
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# If we do that, in situations like:
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#
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# demandimport.enable()
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# ...
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# from foo.bar import mod1
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# with demandimport.deactivated():
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# from foo.bar import mod2
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#
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# mod2 will be imported lazily. (The converse also holds -- whatever finder
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# first gets cached will be used.)
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#
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# Instead, have a global flag the LazyLoader can use.
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global _deactivated
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demandenabled = isenabled()
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if demandenabled:
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_deactivated = True
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try:
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yield
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finally:
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if demandenabled:
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_deactivated = False
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