Mercurial > hg
comparison mercurial/demandimport.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> |
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date | Sun, 19 Jun 2016 02:17:33 +0900 |
parents | c7f89ad87bae |
children | 8960fcb76ca4 |
comparison
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deleted
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29374:7712fcde2d56 | 29375:fcaf20175b1b |
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186 # replace the symbol with the actual module instance at load | 186 # replace the symbol with the actual module instance at load |
187 # time. | 187 # time. |
188 if globalname and isinstance(symbol, _demandmod): | 188 if globalname and isinstance(symbol, _demandmod): |
189 symbol._addref(globalname) | 189 symbol._addref(globalname) |
190 | 190 |
191 def chainmodules(rootmod, modname): | |
192 # recurse down the module chain, and return the leaf module | |
193 mod = rootmod | |
194 for comp in modname.split('.')[1:]: | |
195 if getattr(mod, comp, nothing) is nothing: | |
196 setattr(mod, comp, | |
197 _demandmod(comp, mod.__dict__, mod.__dict__)) | |
198 mod = getattr(mod, comp) | |
199 return mod | |
200 | |
191 if level >= 0: | 201 if level >= 0: |
192 # The "from a import b,c,d" or "from .a import b,c,d" | |
193 # syntax gives errors with some modules for unknown | |
194 # reasons. Work around the problem. | |
195 if name: | 202 if name: |
196 return _hgextimport(_origimport, name, globals, locals, | 203 # "from a import b" or "from .a import b" style |
197 fromlist, level) | 204 rootmod = _hgextimport(_origimport, name, globals, locals, |
198 | 205 level=level) |
199 if _pypy: | 206 mod = chainmodules(rootmod, name) |
207 elif _pypy: | |
200 # PyPy's __import__ throws an exception if invoked | 208 # PyPy's __import__ throws an exception if invoked |
201 # with an empty name and no fromlist. Recreate the | 209 # with an empty name and no fromlist. Recreate the |
202 # desired behaviour by hand. | 210 # desired behaviour by hand. |
203 mn = globalname | 211 mn = globalname |
204 mod = sys.modules[mn] | 212 mod = sys.modules[mn] |
218 return mod | 226 return mod |
219 | 227 |
220 # But, we still need to support lazy loading of standard library and 3rd | 228 # But, we still need to support lazy loading of standard library and 3rd |
221 # party modules. So handle level == -1. | 229 # party modules. So handle level == -1. |
222 mod = _hgextimport(_origimport, name, globals, locals) | 230 mod = _hgextimport(_origimport, name, globals, locals) |
223 # recurse down the module chain | 231 mod = chainmodules(mod, name) |
224 for comp in name.split('.')[1:]: | |
225 if getattr(mod, comp, nothing) is nothing: | |
226 setattr(mod, comp, | |
227 _demandmod(comp, mod.__dict__, mod.__dict__)) | |
228 mod = getattr(mod, comp) | |
229 | 232 |
230 for x in fromlist: | 233 for x in fromlist: |
231 processfromitem(mod, x) | 234 processfromitem(mod, x) |
232 | 235 |
233 return mod | 236 return mod |