Path: ...!3.eu.feeder.erje.net!feeder.erje.net!news.in-chemnitz.de!news.swapon.de!fu-berlin.de!uni-berlin.de!not-for-mail
From: 2QdxY4RzWzUUiLuE@potatochowder.com
Newsgroups: comp.lang.python
Subject: Re: how to discover what values produced an exception?
Date: Sat, 4 May 2024 15:33:00 -0400
Lines: 36
Message-ID: <mailman.6.1714852629.3326.python-list@python.org>
References: <8734qz9ey0.fsf@tudado.org>
 <ZjaNbCKXwgqDOC8R@anomaly>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: news.uni-berlin.de U/m+gcItBuC3j7UqUXJsfAE4rLnWlOkOWKG6yaErtF3g==
Cancel-Lock: sha1:wJAuzhvLkYUYYLWzFN0dTO4pfsw= sha256:tDChsIwkIEXwsvbx0jOXZHj/F0dcsdMdyne4zQDNp1s=
Return-Path: <2QdxY4RzWzUUiLuE@potatochowder.com>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
Authentication-Results: mail.python.org; dkim=pass
 reason="2048-bit key; unprotected key"
 header.d=potatochowder.com header.i=@potatochowder.com
 header.b=gr608v3e; dkim-adsp=pass; dkim-atps=neutral
X-Spam-Status: OK 0.000
X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'this:': 0.03; 'def': 0.04;
 'traceback': 0.04; '(most': 0.05; 'last):': 0.05; 'cases.': 0.09;
 'subject:how': 0.09; 'typeerror:': 0.09;
 'from:addr:2qdxy4rzwzuuilue': 0.16; 'from:addr:potatochowder.com':
 0.16; 'received:136.243': 0.16; 'received:172.58': 0.16;
 'received:www458.your-server.de': 0.16; 'received:your-server.de':
 0.16; 'refuse': 0.16; 'run-time': 0.16; 'subject:values': 0.16;
 'subject:what': 0.16; 'useful.': 0.16; 'wrote:': 0.16; 'python':
 0.16; 'values': 0.17; 'to:addr:python-list': 0.20; 'problem,':
 0.22; 'received:de': 0.23; "isn't": 0.27; 'function': 0.27; '>>>':
 0.28; 'printed': 0.28; "doesn't": 0.32; '"",': 0.32; 'python-
 list': 0.32; 'received:136': 0.32; "i'm": 0.33; 'printing': 0.34;
 'header:In-Reply-To:1': 0.34; 'those': 0.36; 'lists': 0.37;
 "it's": 0.37; 'file': 0.38; 'could': 0.38; 'least': 0.39; 'safe':
 0.39; 'something': 0.40; 'involved': 0.63; 'similar': 0.65;
 'types': 0.67; 'knowing': 0.71; 'discover': 0.80; 'received:88':
 0.84; 'caused': 0.86
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
 d=potatochowder.com; s=default2305; h=In-Reply-To:Content-Type:MIME-Version:
 References:Message-ID:Subject:To:From:Date:Sender:Reply-To:Cc:
 Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date:
 Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID;
 bh=fWc7axUUHiBV+kb9rjkm7QuIg+tUXX0RzeE6l8VzP6k=; b=gr608v3eVWj8ZvOAcHACH5ztT6
 3ZuXGtBNtmphLXBGQcIpUVz7Fe01xz6pE6NYWlM2pdPNc9zi5DX3BLMz5vpktgaiAfcpFpCcWH4h/
 u2sar7ptcWDudCgisF4cwnJPRrC9R+accJiXubRDjv5tRMkf4jt9ZvhFFI7hVlVcSzk/5xSZZK9j+
 ZDftlgwA6SR0tMauezEDHbfL75Kfk3Mkk4ZeHJgECENGbEyUWtqi/y4WYLHLQozxM2mCets8Yfork
 N+miC28kLMWBv9MzOXspCBbUju3JviatYSpru3sAQDksfgBd7F1MGJFy99wFzzdVgiO+Lmcve/ioy
 NHTwleKg==;
Mail-Followup-To: python-list@python.org
Content-Disposition: inline
In-Reply-To: <8734qz9ey0.fsf@tudado.org>
X-Authenticated-Sender: 2QdxY4RzWzUUiLuE@potatochowder.com
X-Virus-Scanned: Clear (ClamAV 0.103.10/27265/Sat May  4 10:23:33 2024)
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.39
Precedence: list
List-Id: General discussion list for the Python programming language
 <python-list.python.org>
List-Unsubscribe: <https://mail.python.org/mailman/options/python-list>,
 <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <https://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <https://mail.python.org/mailman/listinfo/python-list>,
 <mailto:python-list-request@python.org?subject=subscribe>
X-Mailman-Original-Message-ID: <ZjaNbCKXwgqDOC8R@anomaly>
X-Mailman-Original-References: <8734qz9ey0.fsf@tudado.org>
Bytes: 5430

On 2024-05-03 at 10:56:39 -0300,
Johanne Fairchild via Python-list <python-list@python.org> wrote:

> How to discover what values produced an exception?  Or perhaps---why
> doesn't the Python traceback show the values involved in the TypeError?
> For instance:
> 
> --8<-------------------------------------------------------->8---
> >>> (0,0) < 4
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: '<' not supported between instances of 'tuple' and 'int'
> --8<-------------------------------------------------------->8---
> 
> It could have said something like: 
> 
> --8<-------------------------------------------------------->8---
> TypeError: '<' not supported between instances of 'tuple' and 'int'
>   in (0,0) < 4.
> --8<-------------------------------------------------------->8---
> 
> We would know which were the values that caused the problem, which would
> be very helpful.

I'm not disagreeing that knowing the values could be useful in many
cases.  In the general case, though, it's not practical.  Consider a
function like this:

    def f(x, y):
        return g(x) < h(y)

The printed values of x, y, g(x), and h(y) could all be millions of (or
more) glyphs.  Worse, one or more of those values could contain circular
lists or similar structures.  And h or g could have changed x or y.  In
summary, printing run-time values isn't always safe or useful.  At least
printing the types is safe.  In the face of ambiguity, refuse to guess.