Feature Requests item #1454344, was opened at 2006-03-20 09:24
Message generated for change (Comment added) made by gbrandl
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Category: Python Interpreter Core
Group: None
>Status: Closed
>Resolution: Rejected
Priority: 5
Submitted By: kxroberto (kxroberto)
Assigned to: Nobody/Anonymous (nobody)
Summary: Make more out of 'as' : general ad-hoc right-assignment
Initial Comment:
"with EXPR as VAR" introduces 'as' as keyword.
Occupying a new 2-letter kw, Python could maybe make
more out of this:
* it was often asked for transitive assignments to
speed up the interrupted style of typing in Python
* yet transitive left-assignments = += *= ... would
indeed be an impact on pythonic discipline, create bad
readable syntax, which can easyly be confused with ==
etc inside of Expressions. It would be not intuitive,
with what value we are computing. Think e.g. of ugly
things like:
> a = ( 1+ (b.=2/x) )
Now trying a right-hand-assignment method using 'as'
everywhere:
> with open(x) as f:
> f.write(s)
> if re.search(x,s) as m:
> print m.group(1)
> elif re.search(y,s) as m:
> print m.group(1)
> while (x+1 as x) not in l:
> do()
> a = ( 1+ ( 2/x as b ) ), 2+b, 3+b
>
> print 'comment number', (id+1 as id)
* I cannot see any uglyness in this kind of
right-hand-assignment. Its intuitive 'english', speeds
up typing tremendously, the computed thing on left side
is still that, what is in the focus of reading.
And maybe most important: it supports a natural
evolutionary style of thinking: First you think about
what you want compute in expressions, then you can
store aside usefull stuff to somewhere happily.
* 'as'-evolution with extra operator is not too
tempting and clearly separated from the main =
'planning' doctrin
* The operator priority of 'as' right-assignments
should be higher than that of left-assignments and be
next before brackets and commas. Execution order from
left to right - that resolves as expected :
> a += b as c
> l=[ 1 as one, one+1 as two, {key as mykey:3 as three} ]
> d=dict(var1=pi/2 as pi_2, )
The later 'as' would of course set pi_2 in caller's
context.
A transitive 'as' would be more important than having
'is' for the same as '=='. In fact, if "with .. as .."
is possible, but "if .. as .." not, this would appear
as broken syntax design to python newcomers.
Robert
----------------------------------------------------------------------
>Comment By: Georg Brandl (gbrandl)
Date: 2006-03-26 20:42
Message:
Logged In: YES
user_id=849994
Rejecting this for now. It has been proposed on python-dev,
was not commented positively by Guido and won't be possible
without a PEP.
Regarding with .. as: In this context, "as" does _not_
assign the thing on its left to the name on its right. This
would lead to at least some confusion if "if .. as" did this.
----------------------------------------------------------------------
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