To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: I love assert
Date: Tue, 11 Nov 2014 17:34:27 -0500
References: <96c138e4-ab95-4e5f-a0c8-e696b5a926bb@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0
In-Reply-To: <96c138e4-ab95-4e5f-a0c8-e696b5a926bb@googlegroups.com>
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.15697.1415745600.18130.python-list@python.org>
Lines: 32
NNTP-Posting-Host: 2001:888:2000:d::a6
Path: csiph.com!usenet.pasdenom.info!bete-des-vosges.org!feed.ac-versailles.fr!nerim.net!novso.com!newsfeed.xs4all.nl!newsfeed4a.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Xref: csiph.com comp.lang.python:80572

On 11/11/2014 2:40 PM, Peter Cacioppi wrote:
> I get the impression that most Pythonistas aren't as habituated with
> assert statements as I am. Is that just a misimpression on my part?
> If not, is there a good reason to assert less with Python than other
> languages?

We love 'assert' so much that we have 20-30 'assertXYZ' variations in 
unittest.  The statement 'assert expression' is almost equivalent to

if not expression: raise AssertionError('expression')

We have perhaps 100 mostly more specialized exceptions builtin and in 
the stdlib.  There is nearly always a better, more specific exception 
and error message.

> As far as I can tell, Python supports assert perfectly well. When run
> with the optimization flagging, the asserts are truly removed.

Separating tests from main code removes test asserts from the main code. 
  Removal by -0 relegates bare assert to specialized usage.

> I think one needs to take care with some basic assert coding - it's
> not a substitute for unit tests, it doesn't absolve you of normal
> exception responsibilities, and, most of all, it should be used for
> passive inspection and not action. But given these guidelines, I
> still find it very useful as "active comments".

How much usage depends considerably on the programmer.

-- 
Terry Jan Reedy