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From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Interpreting Left to right?
Date: Fri, 24 Jun 2011 17:02:00 -0400
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:8408

On 6/24/2011 4:06 PM, Tycho Andersen wrote:

> tmp = {}
> x['huh'] = tmp # NameEror!
>
> That is, the right hand sides of assignments are evaluated before the
> left hand sides. That is (somehow?) not the case here.

You are parsing "a = b = c" as "a = (b = c)" which works in a language 
in which assignment is an expression, but does not work in Python where 
assignment is a statement. You have to parse it more as "(a = b) = c" 
but that does not work since then the first '=' is not what it seems. It 
is more like "(both a and b) = c". Perhaps best to expand "a = b = c" to 
"a = c; b = c" and see the first as an abbreviation thereof -- just 
delete the 'c;'.

If I have ever used this sort of multiple assignment, it has been for 
simple unambiguous things like "a = b = 0".

-- 
Terry Jan Reedy