Description

serhiy-storchaka

opened on Apr 6, 2018

Issue body actions

BPO	33237
Nosy	@brettcannon, @ncoghlan, @ericsnowcurrently, @serhiy-storchaka
PRs	bpo-33237: Improve AttributeError message for partially initialized module. #6398

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-10-30.11:21:29.153>
created_at = <Date 2018-04-06.15:43:32.578>
labels = ['interpreter-core', 'type-feature', '3.8']
title = 'Improve AttributeError message for partially initialized module'
updated_at = <Date 2018-10-30.11:21:29.152>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2018-10-30.11:21:29.152>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2018-10-30.11:21:29.153>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2018-04-06.15:43:32.578>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 33237
keywords = ['patch']
message_count = 8.0
messages = ['315019', '315020', '315071', '315076', '315136', '315166', '328131', '328895']
nosy_count = 4.0
nosy_names = ['brett.cannon', 'ncoghlan', 'eric.snow', 'serhiy.storchaka']
pr_nums = ['6398']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue33237'
versions = ['Python 3.8']

Activity

1. serhiy-storchaka commented on Apr 6, 2018

   

   serhiy-storchaka

   on Apr 6, 2018

   MemberAuthor

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   Cyclic import usually leads to an AttributeError "module 'spam' has no attribute 'ham'" which usually is confusing because in normal case 'spam.ham' exists, and the user can have no ideas why it is disappeared.

   The proposed PR allows to specialize the AttributeError message for partially initialized module. Any suggestions about the error message?
2. serhiy-storchaka

   added

   3.8 (EOL)end of lifeend of life

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   type-featureA feature request or enhancementA feature request or enhancement

   on Apr 6, 2018
3. ncoghlan commented on Apr 6, 2018

   

   ncoghlan

   on Apr 6, 2018

   Contributor

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   While I like the idea of this change, the "partially initialized" addition is fairly subtle, and relatively easy to miss.

   Perhaps append "(most likely due to a circular import)" to the partially initialized case?:

   AttributeError: partially initialized "module 'spam' has no attribute 'ham' (most likely due to a circular import).
   

   Crucially, for folks encountering the error for the first time, that also introduces them to the main phrase they may want to search for: "circular import".

   The "most likely" weasel wording stems from the fact that the problem won't always be with the circular import - they may have just straight up referenced the wrong module or the wrong attribute name, so the apparently circular import is an error.
4. brettcannon commented on Apr 7, 2018

   

   brettcannon

   on Apr 7, 2018

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   +1 from me for Nick's suggestion.
5. ncoghlan commented on Apr 8, 2018

   

   ncoghlan

   on Apr 8, 2018

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   Oops, just realised my suggested text had an extraneous double quote in it due to a copy-and-paste error. Fixed version:

   AttributeError: partially initialized module 'spam' has no attribute 'ham' (most likely due to a circular import).
   
6. serhiy-storchaka commented on Apr 9, 2018

   

   serhiy-storchaka

   on Apr 9, 2018

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   I have applied the Nick's suggestion. Needed to find a place for new test.

   The code is copied from PyImport_ImportModuleLevelObject(). I'm not happy from how verbose it is. And testing mod.__spec__._initialized adds relatively large overhead for importing already imported module in PyImport_ImportModuleLevelObject(). Is it possible to invent a faster way for checking whether the module is partially imported?
7. ncoghlan commented on Apr 10, 2018

   

   ncoghlan

   on Apr 10, 2018

   Contributor

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   The main idea that comes to mind is to cache a reference to _frozen_importlib._module_locks in the interpreter state, and do a key lookup in there (since any in-progress import should have a lock allocated to it).

   That would be a separate performance issue though - for this issue, we're on an error handling path, so the speed with which the error gets reported isn't critical (although it does technically slow down try/except import fallback chains).
8. serhiy-storchaka commented on Oct 20, 2018

   

   serhiy-storchaka

   on Oct 20, 2018

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   Example:

   $ cat foo.py
   import bar
   bar.baz
   $ cat bar.py
   import foo
   baz = 2
   $ ./python foo.py 
   Traceback (most recent call last):
     File "foo.py", line 1, in <module>
       import bar
     File "/home/serhiy/py/cpython/bar.py", line 1, in <module>
       import foo
     File "/home/serhiy/py/cpython/foo.py", line 2, in <module>
       bar.baz
   AttributeError: module 'bar' has no attribute 'baz'

   Patched:

   $ ./python foo.py 
   Traceback (most recent call last):
     File "foo.py", line 1, in <module>
       import bar
     File "/home/serhiy/py/cpython/bar.py", line 1, in <module>
       import foo
     File "/home/serhiy/py/cpython/foo.py", line 2, in <module>
       bar.baz
   AttributeError: partially initialized module 'bar' has no attribute 'baz' (most likely due to a circular import)
9. serhiy-storchaka commented on Oct 30, 2018

   

   serhiy-storchaka

   on Oct 30, 2018

   MemberAuthor

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   New changeset 3e429dc by Serhiy Storchaka in branch 'master':
   bpo-33237: Improve AttributeError message for partially initialized module. (GH-6398)
   3e429dc
10. serhiy-storchaka

    closed this as completedon Oct 30, 2018
11. ezio-melotti

    transferred this issue fromon Apr 10, 2022

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