Typo hint message for from-imports?

[Jean-Abou-Samra]

BPO	46902
Nosy	@aroberge, @pablogsal, @jean-abou-samra

^{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 = None
created_at = <Date 2022-03-02.20:42:20.452>
labels = ['interpreter-core', 'type-feature', '3.11']
title = 'Typo hint message for from-imports?'
updated_at = <Date 2022-03-03.01:54:35.713>
user = 'https://github.com/Jean-Abou-Samra'

bugs.python.org fields:

activity = <Date 2022-03-03.01:54:35.713>
actor = 'pablogsal'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2022-03-02.20:42:20.452>
creator = 'Jean_Abou_Samra'
dependencies = []
files = []
hgrepos = []
issue_num = 46902
keywords = []
message_count = 2.0
messages = ['414385', '414398']
nosy_count = 3.0
nosy_names = ['aroberge', 'pablogsal', 'Jean_Abou_Samra']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue46902'
versions = ['Python 3.11']

• PR: gh-91058: Add what's new entry for the improvement in commit 7cfbb49fcd4c85f9bab3797302eadf93df490344 #99198

[Jean-Abou-Samra]

See for example:

>>> from pygments.regexopt import regexopt
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name 'regexopt' from 'pygments.regexopt' (/home/jean/repos/pygments/pygments/regexopt.py)
>>> from pygments.regexopt import regex_opt
>>> regexopt
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'regexopt' is not defined. Did you mean: 'regex_opt'?

In Python 3.10, there is a nice helpful error message suggesting
how to correct the typo for NameError and AttributeError. Would
it be possible to have the same for ImportError with 'from import'?

[pablogsal]

I evaluated this, but is considerably more complex than the regular import, because one triggers an attribute error where we have the full module but in the second case we don't have the full module ready, so it requires considerable modifications.

I will investigate again if there is a way that doesn't require lots of changes, but is likely that we unfortunately need to reject this improvement :(

[erlend-aasland]

Pablo's reply hints that the added complexity would not be worth it. I suggest to consider closing this as rejected, unless Pablo found a less complex way :)

[aroberge]

Perhaps it is doable within CPython without too much added code since is something that friendly_traceback can do.

[1]: from pygments.regexopt import regexopt

Traceback (most recent call last):
  Code block [1], line 1
    from pygments.regexopt import regexopt
ImportError: cannot import name 'regexopt' from 'pygments.regexopt'
(C:\Users\Andre.Roberge\AppData\Local\Programs\Python\Python310\lib\site-packages\pygments\regexopt.py)

Did you mean regex_opt?

[2]: why()

Perhaps you meant to import regex_opt (from pygments.regexopt) instead of regexopt

[3] import sys;

[4] 'pygments' in sys.modules
True

[pablogsal]

@aroberge You comment shows that friendly_traceback does it but unfortunately, it doesn't mention how you are proposing us to do it so we cannot evaluate the solution :( Could you add a brief sketch of how you are doing it in friendly_traceback?

[aroberge]

@pablogsal friendly_traceback looks at the list of modules found in sys.modules and, if the desired module is found, it proceeds from there.

The relevant code starts at:
https://github.com/friendly-traceback/friendly-traceback/blob/cdf87b1a623c4afcab4ad869eb29fe885e2d0621/friendly_traceback/runtime_errors/import_error.py#L104

Perhaps the way that the information available to friendly_traceback after an exception has been raised is not yet available to CPython at that point, but I thought I should mention this possibility.

[pablogsal]

@pablogsal friendly_traceback looks at the list of modules found in sys.modules and, if the desired module is found, it proceeds from there.

The relevant code starts at: friendly-traceback/friendly-traceback@cdf87b1/friendly_traceback/runtime_errors/import_error.py#L104

Perhaps the way that the information available to friendly_traceback after an exception has been raised is not yet available to CPython at that point, but I thought I should mention this possibility.

The problem with this approach is that if we do this every time the interpreter raises an ImportError we will slow down the interpreter when someone is catching said exception and continuing so they will have to pay an important (unbounded) cost for a message they won't see. That is what I am trying to circumvent. We cannot also install any exception hooks because of bootstrapping problems and because the interpreter needs to raise them without executing Python in some scenarios.

[aroberge]

Understood; most Python users (myself included) do appreciate this emphasis on speed. Those requiring better traceback analysis can use third-party packages, like friendly_traceback.

[erlend-aasland]

Yeah, I think this approach is not very useful for CPython. A lot of stdlib modules try to import their C implementation first, else fall back to a Python implementation. I think we can safely close this.

[pablogsal]

The fairy of error messages is back! ✨

I found a way to implement this without penalty to control-flow failed imports that are quite clean IMHO:

#98305

Thanks @aroberge for suggesting the idea in the first place. Good things come to those who wait apparently :)