Re: A new to Python question

On Sun, 15 May 2005 08:00:47 +0200, "Fredrik Lundh" <fredrik@xxxxxxxxxxxxxx> wrote:

>M.E.Farmer wrote:
>
>> I said exactly what I meant, the parentheses around the values creates
>> a tuple that you have no reference to!
>
>repeating it doesn't make you right; no extra tuple is created, and the
>parens are part of the syntax:
>
> If the target is a target list enclosed in parentheses or in square
> brackets: The object must be a sequence with the same number
> of items as there are targets in the target list, and its items are
> assigned, from left to right, to the corresponding targets.
>
> http://docs.python.org/ref/assignment.html
>
>(originally, you had to use [] to unpack lists, and () or no parens only
>worked for tuples. the ability to use an arbitrary sequence was added
>in 1.5)
>
Note that (x) without a comma doesn't unpack like [x] however:

>>> (x)= 123,
>>> x
(123,)
>>> [x]= 123,
>>> x
123
>>> (x,)= 123,
>>> x
123
>>> x,= 123,
>>> x
123

Also, BTW,

>>> 123,
(123,)
>>> [123,]
[123]

I.e., that last result is not [(123,)]

There's actually a bunch of context-sensitive things about commas that
you just have to get used to, in lists, tuples, function call arg lists,
subscripts (__getitem__ args), unpacking assignment targets, etc.

>on the other hand, the function you're calling in this example *does*
>create a tuple that you have no reference to after the assignment.
Yeah, but it would create that tuple whether there was an assignment
of the returned result or not. Collecting unconnected facts in one
breath remind me too much of political speeches ;-)
>that doesn't matter, of course, since the tuple is removed by the
>garbage collector immediately after it has been unpacked.
I'm too tired to figure a humorous segue ;-)

Regards,
Bengt Richter
.

Relevant Pages

  • Re: A new to Python question
    ... If the target is a target list enclosed in parentheses or in square ... (originally, you had to use to unpack lists, and () ... create a tuple that you have no reference to after the assignment. ...
    (comp.lang.python)
  • backref customization?
    ... Is it possible to customize backref output so the list of pages on ... which a given reference appears is not printed as ... The documentation lists some customization options such as \backrefsep ... but apparently nothing that would allow to have parentheses or a ...
    (comp.text.tex)
  • [mgross@linux.intel.com: [linux-pm] [patch] pm-qos refresh]
    ... an aggregated target value. ... +changes to the request list or elements of the list. ... QoS dependencies. ... all changes to requirements or notifiers lists ...
    (Linux-Kernel)
  • Re: VS 2005 pb on web site publish
    ... Target "_CheckForInvalidConfigurationAndPlatform" skipped. ... Reference found at search path location ... Could not resolve this reference. ... If this reference is required by your code, you may get compilation ...
    (microsoft.public.dotnet.framework.aspnet)
  • Re: VS 2005 pb on web site publish
    ... Target "_CheckForInvalidConfigurationAndPlatform" skipped. ... Reference found at search path location ... Could not resolve this reference. ... If this reference is required by your code, you may get compilation ...
    (microsoft.public.dotnet.framework.aspnet)