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# demandimport.py - global demand-loading of modules for Mercurial
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#
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# Copyright 2006, 2007 Matt Mackall <mpm@selenic.com>
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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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'''
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demandimport - automatic demandloading of modules
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To enable this module, do:
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import demandimport; demandimport.enable()
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Imports of the following forms will be demand-loaded:
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import a, b.c
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import a.b as c
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from a import b,c # a will be loaded immediately
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These imports will not be delayed:
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from a import *
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b = __import__(a)
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'''
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from __future__ import absolute_import
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import contextlib
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import os
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import sys
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# __builtin__ in Python 2, builtins in Python 3.
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try:
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import __builtin__ as builtins
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except ImportError:
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import builtins
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contextmanager = contextlib.contextmanager
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_origimport = __import__
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nothing = object()
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# Python 3 doesn't have relative imports nor level -1.
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level = -1
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if sys.version_info[0] >= 3:
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level = 0
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_import = _origimport
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def _hgextimport(importfunc, name, globals, *args, **kwargs):
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try:
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return importfunc(name, globals, *args, **kwargs)
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except ImportError:
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if not globals:
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raise
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# extensions are loaded with "hgext_" prefix
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hgextname = 'hgext_%s' % name
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nameroot = hgextname.split('.', 1)[0]
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contextroot = globals.get('__name__', '').split('.', 1)[0]
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if nameroot != contextroot:
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raise
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# retry to import with "hgext_" prefix
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return importfunc(hgextname, globals, *args, **kwargs)
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class _demandmod(object):
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"""module demand-loader and proxy"""
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def __init__(self, name, globals, locals, level=level):
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if '.' in name:
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head, rest = name.split('.', 1)
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after = [rest]
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else:
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head = name
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after = []
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object.__setattr__(self, "_data",
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(head, globals, locals, after, level, set()))
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object.__setattr__(self, "_module", None)
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def _extend(self, name):
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"""add to the list of submodules to load"""
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self._data[3].append(name)
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def _addref(self, name):
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"""Record that the named module ``name`` imports this module.
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References to this proxy class having the name of this module will be
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replaced at module load time. We assume the symbol inside the importing
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module is identical to the "head" name of this module. We don't
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actually know if "as X" syntax is being used to change the symbol name
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because this information isn't exposed to __import__.
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"""
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self._data[5].add(name)
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def _load(self):
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if not self._module:
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head, globals, locals, after, level, modrefs = self._data
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mod = _hgextimport(_import, head, globals, locals, None, level)
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# load submodules
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def subload(mod, p):
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h, t = p, None
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if '.' in p:
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h, t = p.split('.', 1)
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if getattr(mod, h, nothing) is nothing:
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setattr(mod, h, _demandmod(p, mod.__dict__, mod.__dict__))
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elif t:
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subload(getattr(mod, h), t)
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for x in after:
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subload(mod, x)
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# Replace references to this proxy instance with the actual module.
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if locals and locals.get(head) == self:
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locals[head] = mod
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for modname in modrefs:
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modref = sys.modules.get(modname, None)
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if modref and getattr(modref, head, None) == self:
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setattr(modref, head, mod)
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object.__setattr__(self, "_module", mod)
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def __repr__(self):
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if self._module:
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return "<proxied module '%s'>" % self._data[0]
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return "<unloaded module '%s'>" % self._data[0]
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def __call__(self, *args, **kwargs):
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raise TypeError("%s object is not callable" % repr(self))
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def __getattribute__(self, attr):
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if attr in ('_data', '_extend', '_load', '_module', '_addref'):
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return object.__getattribute__(self, attr)
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self._load()
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return getattr(self._module, attr)
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def __setattr__(self, attr, val):
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self._load()
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setattr(self._module, attr, val)
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def _demandimport(name, globals=None, locals=None, fromlist=None, level=level):
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if not locals or name in ignore or fromlist == ('*',):
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# these cases we can't really delay
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return _hgextimport(_import, name, globals, locals, fromlist, level)
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elif not fromlist:
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# import a [as b]
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if '.' in name: # a.b
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base, rest = name.split('.', 1)
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# email.__init__ loading email.mime
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if globals and globals.get('__name__', None) == base:
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return _import(name, globals, locals, fromlist, level)
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# if a is already demand-loaded, add b to its submodule list
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if base in locals:
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if isinstance(locals[base], _demandmod):
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locals[base]._extend(rest)
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return locals[base]
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return _demandmod(name, globals, locals, level)
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else:
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# There is a fromlist.
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# from a import b,c,d
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# from . import b,c,d
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# from .a import b,c,d
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# level == -1: relative and absolute attempted (Python 2 only).
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# level >= 0: absolute only (Python 2 w/ absolute_import and Python 3).
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# The modern Mercurial convention is to use absolute_import everywhere,
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# so modern Mercurial code will have level >= 0.
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# The name of the module the import statement is located in.
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globalname = globals.get('__name__')
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def processfromitem(mod, attr):
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"""Process an imported symbol in the import statement.
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If the symbol doesn't exist in the parent module, it must be a
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module. We set missing modules up as _demandmod instances.
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"""
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symbol = getattr(mod, attr, nothing)
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if symbol is nothing:
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symbol = _demandmod(attr, mod.__dict__, locals, level=1)
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setattr(mod, attr, symbol)
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# Record the importing module references this symbol so we can
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# replace the symbol with the actual module instance at load
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# time.
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if globalname and isinstance(symbol, _demandmod):
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symbol._addref(globalname)
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if level >= 0:
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# Mercurial's enforced import style does not use
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# "from a import b,c,d" or "from .a import b,c,d" syntax. In
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# addition, this appears to be giving errors with some modules
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# for unknown reasons. Since we shouldn't be using this syntax
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# much, work around the problems.
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if name:
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return _hgextimport(_origimport, name, globals, locals,
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fromlist, level)
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mod = _hgextimport(_origimport, name, globals, locals, level=level)
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for x in fromlist:
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processfromitem(mod, x)
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return mod
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# But, we still need to support lazy loading of standard library and 3rd
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# party modules. So handle level == -1.
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mod = _hgextimport(_origimport, name, globals, locals)
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# recurse down the module chain
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for comp in name.split('.')[1:]:
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if getattr(mod, comp, nothing) is nothing:
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setattr(mod, comp,
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_demandmod(comp, mod.__dict__, mod.__dict__))
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mod = getattr(mod, comp)
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for x in fromlist:
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processfromitem(mod, x)
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return mod
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ignore = [
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'__future__',
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'_hashlib',
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'_xmlplus',
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'fcntl',
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'win32com.gen_py',
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'_winreg', # 2.7 mimetypes needs immediate ImportError
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'pythoncom',
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# imported by tarfile, not available under Windows
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'pwd',
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'grp',
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# imported by profile, itself imported by hotshot.stats,
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# not available under Windows
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'resource',
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# this trips up many extension authors
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'gtk',
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# setuptools' pkg_resources.py expects "from __main__ import x" to
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# raise ImportError if x not defined
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'__main__',
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'_ssl', # conditional imports in the stdlib, issue1964
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'_sre', # issue4920
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'rfc822',
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'mimetools',
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# setuptools 8 expects this module to explode early when not on windows
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'distutils.msvc9compiler'
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]
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def isenabled():
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return builtins.__import__ == _demandimport
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def enable():
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"enable global demand-loading of modules"
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if os.environ.get('HGDEMANDIMPORT') != 'disable':
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builtins.__import__ = _demandimport
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def disable():
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"disable global demand-loading of modules"
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builtins.__import__ = _origimport
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@contextmanager
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def deactivated():
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"context manager for disabling demandimport in 'with' blocks"
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demandenabled = isenabled()
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if demandenabled:
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disable()
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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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enable()
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