Re: TypeError expected in an augmented assignment

Newsgroups	comp.lang.python
Date	2014-07-03 02:35 -0700
References	<f1cd7efe-d628-4e96-9ed3-79d9a212f768@googlegroups.com> <mailman.11432.1404356297.18130.python-list@python.org> <55f74a23-95ea-4be1-950d-e57e645dab1a@googlegroups.com> <mailman.11446.1404376617.18130.python-list@python.org>
Message-ID	<6ed679b1-c6e1-408e-8167-476b169fa2eb@googlegroups.com> (permalink)
Subject	Re: TypeError expected in an augmented assignment
From	candide <c.candide@laposte.net>

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> >From that link:
> 
> 
> 
> """
> 
> An augmented assignment expression like x += 1 can be rewritten as x =
> 
> x + 1 to achieve a similar, but not exactly equal effect. In the
> 
> augmented version, x is only evaluated once. Also, when possible, the
> 
> actual operation is performed in-place, meaning that rather than
> 
> creating a new object and assigning that to the target, the old object
> 
> is modified instead.
> 
> """
> 
> 
> 
> The significance here is that the augmented assignment may not
> 
> necessarily be at all comparable to the non-augmented version, but
> 
> ought to have *approximately* the same *intention*. 


This is not my reading. 




> 
> of situations where the two will differ, eg when there are multiple
> 
> references to the same object:
> 
> 
> 
> >>> a = b = [1,2]
> 
> >>> a += [3]
> 
> >>> a,b
> 
> ([1, 2, 3], [1, 2, 3])
> 
> >>> a = a + [4]
> 
> >>> a,b
> 
> ([1, 2, 3, 4], [1, 2, 3])
> 
> 

OK but this behavior is in conformance with the Reference Manual (cf. your quote above : "when possible, the actual operation is performed in-place"). This is not my point because the doc explictly claims that "an augmented assignment [...] performs the binary operation specific to the type of assignment on the two operands".

Thread

TypeError expected in an augmented assignment candide <c.candide@laposte.net> - 2014-07-02 19:39 -0700
  Re: TypeError expected in an augmented assignment Terry Reedy <tjreedy@udel.edu> - 2014-07-02 22:57 -0400
    Re: TypeError expected in an augmented assignment candide <c.candide@laposte.net> - 2014-07-03 00:51 -0700
      Re: TypeError expected in an augmented assignment Chris Angelico <rosuav@gmail.com> - 2014-07-03 18:36 +1000
        Re: TypeError expected in an augmented assignment candide <c.candide@laposte.net> - 2014-07-03 02:35 -0700
          Re: TypeError expected in an augmented assignment Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-07-03 13:43 +0100

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