Mercurial > hg
view mercurial/__init__.py @ 29375:fcaf20175b1b
demandimport: delay loading for "from a import b" with absolute_import
Before this patch, "from a import b" doesn't delay loading module "b",
if absolute_import is enabled, even though "from . import b" does.
For example:
- it is assumed that extension X has "from P import M" for module M
under package P with absolute_import feature
- if importing module M is already delayed before loading extension
X, loading module M in extension X is delayed until actually
referring
util, cmdutil, scmutil or so of Mercurial itself should be
imported by "from . import M" style before loading extension X
- otherwise, module M is loaded immediately at loading extension X,
even if extension X itself isn't used at that "hg" command invocation
Some minor modules (e.g. filemerge or so) of Mercurial itself
aren't imported by "from . import M" style before loading
extension X. And of course, external libraries aren't, too.
This might cause startup performance problem of hg command, because
many bundled extensions already enable absolute_import feature.
To delay loading module for "from a import b" with absolute_import
feature, this patch does below in "from a (or .a) import b" with
absolute_import case:
1. import root module of "name" by system built-in __import__
(referred as _origimport)
2. recurse down the module chain for hierarchical "name"
This logic can be shared with non absolute_import
case. Therefore, this patch also centralizes it into chainmodules().
3. and fall through to process elements in "fromlist" for the leaf
module of "name"
Processing elements in "fromlist" is executed in the code path
after "if _pypy: .... else: ..." clause. Therefore, this patch
replaces "if _pypy:" with "elif _pypy:" to share it.
At 4f1144c3c72b introducing original "work around" for "from a import
b" case, elements in "fromlist" were imported with "level=level". But
"level" might be grater than 1 (e.g. level=2 in "from .. import b"
case) at demandimport() invocation, and importing direct sub-module in
"fromlist" with level grater than 1 causes unexpected result.
IMHO, this seems main reason of "errors for unknown reason" described
in 4f1144c3c72b, and we don't have to worry about it, because this
issue was already fixed by 78d05778907b.
This is reason why this patch removes "errors for unknown reasons"
comment.
author | FUJIWARA Katsunori <foozy@lares.dti.ne.jp> |
---|---|
date | Sun, 19 Jun 2016 02:17:33 +0900 |
parents | b3a677c82a35 |
children | b4d117cee636 |
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# __init__.py - Startup and module loading logic for Mercurial. # # Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com> # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. from __future__ import absolute_import import imp import os import sys import zipimport from . import ( policy ) __all__ = [] modulepolicy = policy.policy # Modules that have both Python and C implementations. See also the # set of .py files under mercurial/pure/. _dualmodules = set([ 'mercurial.base85', 'mercurial.bdiff', 'mercurial.diffhelpers', 'mercurial.mpatch', 'mercurial.osutil', 'mercurial.parsers', ]) class hgimporter(object): """Object that conforms to import hook interface defined in PEP-302.""" def find_module(self, name, path=None): # We only care about modules that have both C and pure implementations. if name in _dualmodules: return self return None def load_module(self, name): mod = sys.modules.get(name, None) if mod: return mod mercurial = sys.modules['mercurial'] # The zip importer behaves sufficiently differently from the default # importer to warrant its own code path. loader = getattr(mercurial, '__loader__', None) if isinstance(loader, zipimport.zipimporter): def ziploader(*paths): """Obtain a zipimporter for a directory under the main zip.""" path = os.path.join(loader.archive, *paths) zl = sys.path_importer_cache.get(path) if not zl: zl = zipimport.zipimporter(path) return zl try: if modulepolicy == 'py': raise ImportError() zl = ziploader('mercurial') mod = zl.load_module(name) # Unlike imp, ziploader doesn't expose module metadata that # indicates the type of module. So just assume what we found # is OK (even though it could be a pure Python module). except ImportError: if modulepolicy == 'c': raise zl = ziploader('mercurial', 'pure') mod = zl.load_module(name) sys.modules[name] = mod return mod # Unlike the default importer which searches special locations and # sys.path, we only look in the directory where "mercurial" was # imported from. # imp.find_module doesn't support submodules (modules with "."). # Instead you have to pass the parent package's __path__ attribute # as the path argument. stem = name.split('.')[-1] try: if modulepolicy == 'py': raise ImportError() modinfo = imp.find_module(stem, mercurial.__path__) # The Mercurial installer used to copy files from # mercurial/pure/*.py to mercurial/*.py. Therefore, it's possible # for some installations to have .py files under mercurial/*. # Loading Python modules when we expected C versions could result # in a) poor performance b) loading a version from a previous # Mercurial version, potentially leading to incompatibility. Either # scenario is bad. So we verify that modules loaded from # mercurial/* are C extensions. If the current policy allows the # loading of .py modules, the module will be re-imported from # mercurial/pure/* below. if modinfo[2][2] != imp.C_EXTENSION: raise ImportError('.py version of %s found where C ' 'version should exist' % name) except ImportError: if modulepolicy == 'c': raise # Could not load the C extension and pure Python is allowed. So # try to load them. from . import pure modinfo = imp.find_module(stem, pure.__path__) if not modinfo: raise ImportError('could not find mercurial module %s' % name) mod = imp.load_module(name, *modinfo) sys.modules[name] = mod return mod # We automagically register our custom importer as a side-effect of loading. # This is necessary to ensure that any entry points are able to import # mercurial.* modules without having to perform this registration themselves. if not any(isinstance(x, hgimporter) for x in sys.meta_path): # meta_path is used before any implicit finders and before sys.path. sys.meta_path.insert(0, hgimporter())