Waffling (was Re: single-line terinary operators considered harmful)

Stephen Horne intentionally at blank.co.uk
Thu Mar 6 20:28:19 CET 2003


On Thu, 6 Mar 2003 13:03:50 -0700, Steven Taschuk
<staschuk at telusplanet.net> wrote:

>Certainly Python's guaranteed evaluation and execution order is
>very comfortable.  There is the occasional oddity:
>	d = {}
>	i = 3
>	i = d[i] = i+1
>has a surprising (to me) result.  But this isn't good style anyway.

I wondered what you were talking about - until I noticed that...

>>> d={}
>>> i=3
>>> i=d[i]=i+1
>>> i
4             <- this was expected
>>> d[i]
4             <- this was expected
>>> d
{4: 4}        <- pardon? - why not {3: 4}


I'm not sure I understand it, but I imagine it has to do with '='
being n-ary (n >= 2) non-associative (rather than binary
right-associative). Maybe the assigns are done left-to-right, even
though the rightmost item is the source and must be evaluated first?

-- 
steve at ninereeds dot fsnet dot co dot uk




More information about the Python-list mailing list