Tim Peters writes:
> [Stephen J. Turnbull[
> > No. It's equivalent to
> >
> > =
> > =
> > =
> >
> > and the order matters because the s may have side effects.
>
> This is tricky stuff.
Thank you, and Guido, for the correction.
___
James has suggested that Python be enhanced so that
>>> a, b += c, d
is a short-hand for
>>> a += c
>>> b += d
Myself, James and Matthew wrote
>> > Does it IN PRACTICE bring sufficient benefits to users?
>> I found myself needing this when I was writing a monte-carlo
>> simulation in python that
On Sun, Aug 26, 2018, 9:24 PM James Lu wrote:
> Hi Johnathan
>
> I echo your points. Indeed, the PEP referenced to refers to a "tuple
> expression" in the grammatical and not the programmatic sense.
>
> Finally, here's something that surprised me a little bit
>
> >>> x = [1, 2]; id(x)
> 140161160
On Sun, Aug 26, 2018 at 07:50:49PM +0100, Jonathan Fine wrote:
> Hi James and Steve
>
> Myself and Steve wrote:
>
> >> Notice that '+=' creates uses the same object when the object is a
> >> list, but creates a new object. This raises the question: Why and how
> >> does Python behave in this way?
[Kirill Balunov]
It may be worth taking a look at + and +=. However, the semantic
difference is due to the dunder add and dunder iadd methods-
necessary for supporting both mutable and immutable sequences. See my
earlier mail for discussion on this topic.
By the way,
> the absence of literals fo
Hi Johnathan
I echo your points. Indeed, the PEP referenced to refers to a "tuple
expression" in the grammatical and not the programmatic sense.
Finally, here's something that surprised me a little bit
>>> x = [1, 2]; id(x)
140161160364616
>>> x += [3, 4]; id(x)
140161160364616
>>> x = (1, 2);
Hi James and Steve
Myself and Steve wrote:
>> Notice that '+=' creates uses the same object when the object is a
>> list, but creates a new object. This raises the question: Why and how
>> does Python behave in this way?
> Lists are mutable and can be modified in place. Tuples are immutable and
вс, 26 авг. 2018 г. в 14:53, Stephen J. Turnbull <
turnbull.stephen...@u.tsukuba.ac.jp>:
> [...]
>
> This isn't consistent with the normal behavior of Python sequences:
>
> $ python3.6
> >>> (1,2) + (3,4)
> (1, 2, 3, 4)
>
> That is, "+" means something different for sequences. Furthermore,
> the
[James Lu]
> > Currently, is = = = always equivalent
> > to = ; = ; = ?
[Stephen J. Turnbull[
> No. It's equivalent to
>
> =
> =
> =
>
> and the order matters because the s may have side effects.
This is tricky stuff. In fact the rightmost expression is evaluated once,
On Sun, Aug 26, 2018 at 06:19:36PM +0100, Jonathan Fine wrote:
> Finally, here's something that surprised me a little bit
>
> >>> x = [1, 2]; id(x)
> 140161160364616
> >>> x += [3, 4]; id(x)
> 140161160364616
> >>> x = (1, 2); id(x)
> 140161159928520
> >>> x += (3, 4); id(x)
> 140161225906440
>
James Lu writes:
> Currently, is = = = always equivalent
> to = ; = ; = ?
No. It's equivalent to
=
=
=
and the order matters because the s may have side effects.
Not sure where the rest of your message was going; it mostly just
seemed to repeat examples from earlier
Hi James
Thank you for your message. I have some general, background comments.
However, the question remains: Does your proposal sit well with the
rest of Python?
By the way, I've just found a nice article:
http://treyhunner.com/2018/03/tuple-unpacking-improves-python-code-readability/
You wrote
Steve and Johnathan, it seems like we're on the same page.
Currently, is = = = always equivalent
to = ; = ; = ?
When there are a tuple or list of names on the left hand side (ex.
`a, b` or `(a, b)` or `[a, b]`), unpack the right hand side into
values and perform the augmented assignment on
James Lu writes:
> I propose we apply PEP 3132 to PEP 203. That is, for every statement where
> " = " is valid I propose "lhs += rhs" should also be
> valid.
>
> Simple example:
> a = 0
> b = 0
> a, b += 1, 2
> # a is now 1
> # b is now 2
This isn't consistent with the normal behavior
Hi James
Thank you for the simple example. It makes discussing your proposal
much easier. I hope you don't mind, I'll modify it a little to make
the semantics clearer, at least to me.
Here it is.
init = (10, 20)
incr = (1, 2)
(a, b) = init
# Now, (a, b) == (10, 20)
a, b += incr
# Now (a, b) ==
I propose we apply PEP 3132 to PEP 203. That is, for every statement where
" = " is valid I propose "lhs += rhs" should also be valid.
Simple example:
a = 0
b = 0
a, b += 1, 2
# a is now 1
# b is now 2
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