[issue31642] None value in sys.modules no longer blocks import

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed
versions:  -Python 3.8

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[issue31642] None value in sys.modules no longer blocks import

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:


New changeset 6f059ab80a351a7dd85cc57c5ca240f817a79c5d by Serhiy Storchaka in 
branch '3.6':
[3.6] bpo-31642: Restore blocking "from" import by setting None in sys.modules. 
(GH-3834). (#3923)
https://github.com/python/cpython/commit/6f059ab80a351a7dd85cc57c5ca240f817a79c5d


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[issue31642] None value in sys.modules no longer blocks import

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
pull_requests: +3896

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[issue31642] None value in sys.modules no longer blocks import

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:


New changeset f07e2b64df6304a36fb5e29397d3c77a7ba17704 by Serhiy Storchaka in 
branch 'master':
bpo-31642: Restore blocking "from" import by setting None in sys.modules. 
(#3834)
https://github.com/python/cpython/commit/f07e2b64df6304a36fb5e29397d3c77a7ba17704


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[issue31642] None value in sys.modules no longer blocks import

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

PR 3834 provide possible solution of this issue.

Initially import errors were silenced for solving issue15715. An import error 
raised when import was blocked by setting None in sys.modules was not silenced 
because it has different error message. I don't know whether this was 
intentional. In issue15767 (5fdb8c897023) the error message test was replaced 
by the type test, and that exception become silenced (I suppose it was not 
intentional).

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[issue31642] None value in sys.modules no longer blocks import

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
keywords: +patch
pull_requests: +3815
stage: needs patch -> patch review

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[issue31642] None value in sys.modules no longer blocks import

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

This is a side effect of issue15767. The exception is raised in _find_and_load, 
but it is always silenced in _handle_fromlist.

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[issue31642] None value in sys.modules no longer blocks import

[Barry A. Warsaw]

Change by Barry A. Warsaw :


--
nosy: +barry

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[issue31642] None value in sys.modules no longer blocks import

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
nosy: +serhiy.storchaka

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[issue31642] None value in sys.modules no longer blocks import

[Christian Heimes]

Change by Christian Heimes :


--
stage:  -> needs patch
type:  -> behavior

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[issue31642] None value in sys.modules no longer blocks import

[Christian Heimes]

Change by Christian Heimes :


--
nosy: +brett.cannon, eric.snow, ncoghlan

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[issue31642] None value in sys.modules no longer blocks import

[Christian Heimes]

New submission from Christian Heimes :

Since Python 3.6, the blocking of imports is broken for 'from package import 
module' imports.

$ mkdir a
$ touch a/__init__.py a/b.py

>>> import sys
>>> sys.modules['a.b'] = None
>>> from a import b
>>> b is None
True
>>> import a.b
Traceback (most recent call last):
  File "", line 1, in 
ModuleNotFoundError: import of 'a.b' halted; None in sys.modules

Tests with Python 2.7 to master:

$ python2.7 -c "from a import b; print(b)"

$ python2.7 -c "import sys; sys.modules['a.b'] = None; from a import b"
Traceback (most recent call last):
  File "", line 1, in 
ImportError: cannot import name b
$ python2.7 -c "import sys; sys.modules['a.b'] = None; from a import b"
Traceback (most recent call last):
  File "", line 1, in 
ImportError: cannot import name b
$ python3.4 -c "import sys; sys.modules['a.b'] = None; from a import b"
Traceback (most recent call last):
  File "", line 1, in 
ImportError: import of 'a.b' halted; None in sys.modules
$ python3.5 -c "import sys; sys.modules['a.b'] = None; from a import b"
Traceback (most recent call last):
  File "", line 1, in 
ImportError: import of 'a.b' halted; None in sys.modules
$ python3.6 -c "import sys; sys.modules['a.b'] = None; from a import b"
$ ./python -c "import sys; sys.modules['a.b'] = None; from a import b"

--
components: Interpreter Core
keywords: 3.6regression
messages: 303356
nosy: christian.heimes
priority: normal
severity: normal
status: open
title: None value in sys.modules no longer blocks import
versions: Python 3.6, Python 3.7, Python 3.8

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