Improving KeyError exception

[zingero]

BPO	42177
Nosy	@terryjreedy, @zingero

^{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 2020-10-30.23:35:37.940>
created_at = <Date 2020-10-27.20:43:09.360>
labels = ['type-feature', '3.10']
title = 'Improving KeyError exception'
updated_at = <Date 2020-10-30.23:35:37.938>
user = 'https://github.com/zingero'

bugs.python.org fields:

activity = <Date 2020-10-30.23:35:37.938>
actor = 'terry.reedy'
assignee = 'none'
closed = True
closed_date = <Date 2020-10-30.23:35:37.940>
closer = 'terry.reedy'
components = []
creation = <Date 2020-10-27.20:43:09.360>
creator = 'zingero'
dependencies = []
files = []
hgrepos = []
issue_num = 42177
keywords = []
message_count = 2.0
messages = ['379801', '380013']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'zingero']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue42177'
versions = ['Python 3.10']

[zingero]

Hi all,

As a Python developer, I encountered lots of blurry exception messages in the product logs such as:
<time and date> <process name> <log severity> Failed to do something. Exception: 'some key'

I believe printing the key name without explaining the exception itself is bad (explicit is better than implicit).

Thus, after forking the repository, I added a short explanation about the Exception.
Now, it looks like:

>>> try:
...     {}['some key']
... except Exception as e:
...     print(e)
... 
Missing key: some key

I'm a newbie in a contribution to CPython, so please let me know if the idea behind my commit is good. If not, please explain how can I improve my commit so it'll be pulled later to the main branch.

zingero@8c9e5d9

Regards,
Orian.

[terryjreedy]

Printing an exception is defined as printing the exception message, which currently is e.args[0]. We will not change that as it would break code worldwide. To print more, the class name can be used directly or as a key into a dict of replacements or replacement functions.

Questions and vague ideas should be directed to python-list. Fleshed out ideas can go to python-ideas.

>>> {}['d']
Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    {}['d']
KeyError: 'd'

>>> try:
	{}['d']
except Exception as e:
	print(e)
	
'd'

>>> try:
	{}['d']
except Exception as e:
	print(e.args)

('d',)

>>> try:
	{}['d']
except Exception as e:
	print(f'{e.__class__.__name__}: {e}')  # Reproduce standard report.

KeyError: 'd'