Interpreting Left to right?
Terry Reedy
tjreedy at udel.edu
Fri Jun 24 17:02:00 EDT 2011
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
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