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Date: Sun, 11 Nov 2012 18:21:32 -0600
From: Tim Chase <python.list@tim.thechases.com>
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To: Steven D'Aprano <steve+comp.lang.python@pearwood.info>
Subject: Re: List comprehension for testing **params
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On 11/11/12 17:18, Steven D'Aprano wrote:
> but that leaves you with the next two problems:
> 
> 2) Fixing the assert still leaves you with the wrong exception. You 
> wouldn't raise a ZeroDivisionError, or a UnicodeDecodeError, or an IOError 
> would you? No of course not. So why are you suggesting raising an 
> AssertionError? That is completely inappropriate, the right exception to 
> use is TypeError. Don't be lazy and treat assert as a quick and easy way 
> to get exceptions for free.

I'd say that it depends on whether the dictionary/kwargs gets
populated from user-supplied data (whether mail, a file, direct
input, etc), or whether it's coder-supplied.

I like to think of "assert" as a "hey, you bone-headed programmer,
you did something that violated conditions for using this code
properly!" and as such, entirely appropriate to use in the
coder-supplied case.  This rolls into...

> 3) Asserts are not guaranteed to run. Never, never, never use assert to 
> test function arguments supplied by the caller, because you have no 
> control over whether or not the asserts will even be called.

where, once the programmer is satisfied that the code runs, meeting
all the appropriate tests/assertions, the assertions can then be
turned off (if one really cares that much; can't say I've done it
more than a couple times, mostly out of experimentation/testing to
see if it made any grave difference in performance).  I think you
intend this in your

> Or for testing things which "can't possibly fail". But of
> course, since what can't go wrong does, you sometimes still want
> to test things.

-tkc