[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Brett Cannon]

Brett Cannon  added the comment:

Sorry, you're right; I forgot importlib got it "right" while import got it 
"wrong". :)

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Miro Hrončok]

Miro Hrončok  added the comment:

For the record, looking at https://docs.python.org/3.9/whatsnew/3.9.html I had 
an impression that this also affects regular imports, as described in 
https://bugzilla.redhat.com/show_bug.cgi?id=1791769#c2 -- if that's not that 
case, I'm sorry.

Anyway, I get your point of "next 30 years of Python".

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Brett Cannon]

Brett Cannon  added the comment:

The problem with the hybrid exception is that importlib would then still raise 
a different exception from import itself, so the discrepancy would persist. And 
if you updated import you could then break people in another way where they 
were catching ValueError and ImportError separately for different cases and now 
they would potentially catch the wrong exception for that ValueError case.

Basically changing what exceptions get raised sucks as someone is almost 
inevitably broken. But since import and importlib strive to mirror each other 
as much as possible and be drop-in replacements, the consistency for the next 
30 years of Python's life is more important I think than the case of:

1. Someone using importlib.import_module()
2. Who is specifically worried about relative imports going too far and no 
other import-related import and thus only catching ValueError and not 
ImportError
3. And are supporting older versions of Python
4. And will have a difficult time updating their `except` clause to now also 
capture ImportError

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Miro Hrončok]

Miro Hrončok  added the comment:

I know that raising a DeprecationWarning here is most likely not possible or 
too black-magical to do. My intention was not to be harsh, sorry about that. I 
just wanted to point out that a backwards incompatible behavior like this 
without a (possible) deprecation warning might not counterweigh the gain of 
raising the logical exception type. As a compromise, I proposed to raise a 
hybrid that inherits from both.

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Brett Cannon]

Brett Cannon  added the comment:

There's no deprecation warning because how do you warn about that? You raise 
DeprecationWarning about an exception you have yet to raise?

And I personally think calling this unfair is a bit harsh.

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Miro Hrončok]

Miro Hrončok  added the comment:

While raising ImportError certainly makes much more sense in this case, this 
change is backwards incompatible and there was no DeprecationWarning. I don't 
consider that fair.

As a certain compromise, we could maybe raise a custom ImportError+ValueError 
offspring (e.g. BeyondToplevelImportError)?

If feeling fancy, we could rise a DeprecationWarning when 
issublcass(BeyondToplevelImportError, ValueError) is used?

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nosy: +hroncok

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Brett Cannon]

Change by Brett Cannon :


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

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[miss-islington]

miss-islington  added the comment:


New changeset c5fa44944ee0a31a12b9a70776c7cb56c4dc39a2 by Miss Islington (bot) 
(Ngalim Siregar) in branch 'master':
bpo-37444: Update differing exception between builtins and importlib (GH-14869)
https://github.com/python/cpython/commit/c5fa44944ee0a31a12b9a70776c7cb56c4dc39a2


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nosy: +miss-islington

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Joannah Nanjekye]

Change by Joannah Nanjekye :


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nosy:  -nanjekyejoannah

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Raymond Hettinger]

Raymond Hettinger  added the comment:

> I think this should be an ImportError 

I also think ImportError is what people would expect when an import fails.

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Ngalim Siregar]

Change by Ngalim Siregar :


--
keywords: +patch
pull_requests: +14657
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/14869

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Joannah Nanjekye]

Change by Joannah Nanjekye :


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nosy: +nanjekyejoannah

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Nick Coghlan]

Nick Coghlan  added the comment:

ImportError sounds right to me.

We already raise that just above this for the "no dots at all" case, so also 
raising it for the "not enough dots" case makes more sense than leaving them 
different.

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Serhiy Storchaka]

Change by Serhiy Storchaka :


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nosy: +serhiy.storchaka

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Brett Cannon]

Brett Cannon  added the comment:

import.c code raising the exception: 
https://github.com/python/cpython/blob/f9f8e3ce709ceb15c8db8c8dde940daf1febf13d/Python/import.c#L1675-L1677

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Brett Cannon]

Brett Cannon  added the comment:

I think this should be an ImportError and so that means builtins.__import__() 
is wrong. Anyone want to argue for the other side?

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Brett Cannon]

Brett Cannon  added the comment:

Importllib code raising the exception is 
https://github.com/python/cpython/blob/f9f8e3ce709ceb15c8db8c8dde940daf1febf13d/Lib/importlib/_bootstrap.py#L874-L876
 .

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[issue37444] Differing exception between builtins and importlib when importing beyond top-level package

[Brett Cannon]

New submission from Brett Cannon :

builtins.__import__() raises ValueError (as it did in Python 2.7) while 
importlib.__import__() raises ImportError (which makes more sense to me).

Found by Ben Lewis.

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components: Interpreter Core, Library (Lib)
messages: 346855
nosy: Ben Lewis2, brett.cannon, eric.snow, ncoghlan
priority: normal
severity: normal
status: open
title: Differing exception between builtins and importlib when importing beyond 
top-level package
versions: Python 3.8, Python 3.9

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