The "in"-statement - python-ideas

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Message from discussion The "in"-statement
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From: Joshua Landau <joshua.landau...@gmail.com>
Date: Mon, 5 Nov 2012 22:05:33 +0000
Message-ID: <CAN1F8qWWoi4VJUdVB_Nqhf70fJwjS6Mu_US3JZnpHEbNchv...@mail.gmail.com>
To: Bruce Leban <br...@leapyear.org>
Cc: python-ideas <python-id...@python.org>
Subject: Re: [Python-ideas] The "in"-statement
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On 5 November 2012 19:47, Bruce Leban <br...@leapyear.org> wrote:

> On Mon, Nov 5, 2012 at 11:28 AM, Markus Unterwaditzer <
> mar...@unterwaditzer.net> wrote:
>
>> While mocking objects, i got annoyed by the following code pattern i had
>> to
>> use when modifying multiple attributes on a single object::
>>
>>     obj.first_attr = "value"
>>     obj.second_attr = "value2"
>>
>>     some_other = "lel"
>>
>> I thought it would be neat if i could do::
>>
>>     in obj:
>>         first_attr = "value"
>>         second_attr = "value2"
>>
>>     some_other = "lel"  # indenting this would cause it to appear as an
>> attribute of obj
>>
>
> Hard to read, error-prone and ill-defined. Does it create new attributes
> or only change existing ones? What about identifiers on right hand sides?
> What would
>     third_attr = lambda: first_attr
> do?
>

My solution has always been:

.third_attr = lambda: .first_attr
.fourth_attr = not_attr

Although a single "." is hard for some [weaklings; pah!] to see.

It has exactly one use-case in my opinion:
def m(self, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u,
v, w, x, y, z):
    in self:
        .a, .b, .c, .d, .e, .f, .g, .h, .i, .j, .k, .l, .m, .n, .o, .p, .q,
.r, .s, .t, .u, .v, .w, .x, .y, .z = \
            a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u,
v, w, x, y, z

....not that having an excuse to do this is a good thing...

And this is easy enough:
>

> def multi_setattr(obj, **kwargs):
>     for k in kwargs:
>         setattr(obj, k, kwargs[k])
>
> multi_setattr(obj,
>     first_attr = "value",
>     second_attr = "value2")
>

TYVM for this, I'd never have thought of it.

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On 5 November 2012 19:47, Bruce Leban <span dir=3D"ltr">&lt;<a href=3D"mail=
to:br...@leapyear.org" target=3D"_blank">br...@leapyear.org</a>&gt;</span> =
wrote:<div class=3D"gmail_extra"><div class=3D"gmail_quote"><blockquote cla=
ss=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left-width:1px;=
border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex=
">

<div class=3D"gmail_quote"><div class=3D"im">On Mon, Nov 5, 2012 at 11:28 A=
M, Markus Unterwaditzer <span dir=3D"ltr">&lt;<a href=3D"mailto:markus@unte=
rwaditzer.net" target=3D"_blank">mar...@unterwaditzer.net</a>&gt;</span> wr=
ote:<br>

<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-=
left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;p=
adding-left:1ex">

While mocking objects, i got annoyed by the following code pattern i had to=
<br>
use when modifying multiple attributes on a single object::<br>
<br>
=A0 =A0 obj.first_attr =3D &quot;value&quot;<br>
=A0 =A0 obj.second_attr =3D &quot;value2&quot;<br>
<br>
=A0 =A0 some_other =3D &quot;lel&quot;<br>
<br>
I thought it would be neat if i could do::<br>
<br>
=A0 =A0 in obj:<br>
=A0 =A0 =A0 =A0 first_attr =3D &quot;value&quot;<br>
=A0 =A0 =A0 =A0 second_attr =3D &quot;value2&quot;<br>
<br>
=A0 =A0 some_other =3D &quot;lel&quot; =A0# indenting this would cause it t=
o appear as an attribute of obj<br></blockquote><div><br></div></div><div>H=
ard to read, error-prone and ill-defined. Does it create new attributes or =
only change existing ones? What about identifiers on right hand sides? What=
 would</div>



<div>=A0 =A0 third_attr =3D lambda: first_attr</div><div>do?</div></div></b=
lockquote><div>=A0</div><div>My solution has always been:</div><div><br></d=
iv><div>.third_attr =3D lambda: .first_attr</div><div>.fourth_attr =3D not_=
attr</div>

<div><br></div><div>Although a single &quot;.&quot; is hard for some [weakl=
ings; pah!] to see.</div><div><br></div><div>It has exactly one use-case in=
 my opinion:</div><div>def m(self, a, b, c, d, e, f, g, h, i, j, k, l, m, n=
, o, p, q, r, s, t, u, v, w, x, y, z):</div>

<div>=A0 =A0 in self:</div><div>=A0 =A0 =A0 =A0 .a, .b, .c, .d, .e, .f, .g,=
 .h, .i, .j, .k, .l, .m, .n, .o, .p, .q, .r, .s, .t, .u, .v, .w, .x, .y, .z=
 =3D \</div><div>=A0 =A0 =A0 =A0 =A0 =A0 a, b, c, d, e, f, g, h, i, j, k, l=
, m, n, o, p, q, r, s, t, u, v, w, x, y, z</div>

<div><br></div><div>....not that having an excuse to do this is a good thin=
g...</div><div><br></div><blockquote class=3D"gmail_quote" style=3D"margin:=
0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);=
border-left-style:solid;padding-left:1ex">

<div class=3D"gmail_quote"><div>And this is easy enough:</div></div></block=
quote><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;b=
order-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:s=
olid;padding-left:1ex">

<div class=3D"gmail_quote"><div><br></div><div>def multi_setattr(obj, **kwa=
rgs):</div><div>=A0 =A0 for k in kwargs:</div><div>=A0 =A0 =A0 =A0 setattr(=
obj, k, kwargs[k])=A0</div>

<div><br></div><div>multi_setattr(obj,</div><div>=A0 =A0 first_attr =3D &qu=
ot;value&quot;,</div><div>=A0 =A0 second_attr =3D &quot;value2&quot;)</div>=
</div></blockquote><div><br></div><div>TYVM for this, I&#39;d never have th=
ought of it.=A0</div>

</div></div>

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