meaning of: line, =

[Rustom Mody]

On Thursday, February 5, 2015 at 10:15:29 PM UTC+5:30, Rustom Mody wrote:
> On Thursday, February 5, 2015 at 9:39:27 PM UTC+5:30, Ian wrote:
> > On Thu, Feb 5, 2015 at 2:40 AM, Steven D'Aprano wrote:
> > > Devin Jeanpierre wrote:
> > >
> > >> On Wed, Feb 4, 2015 at 1:18 PM, Chris Angelico wrote:
> > >>> On Thu, Feb 5, 2015 at 4:36 AM, Peter Otten  wrote:
> > >>>> Another alternative is to put a list literal on the lefthand side:
> > >>>>
> > >>>>>>> def f(): yield 42
> > >>>>
> > >>>> ...
> > >>>>>>> [result] = f()
> > >>>>>>> result
> > >>>> 42
> > >>>
> > >>> Huh, was not aware of that alternate syntax.
> > >>
> > >> Nor are most people. Nor is Python, in some places -- it seems like
> > >> people forgot about it when writing some bits of the grammar.
> > >
> > > Got an example where you can use a,b but not [a,b] or (a,b)?
> > 
> > >>> def f(a, (b, c)):
> > ...     print a, b, c
> 
> What the hell is that?!
> First I am hearing/seeing it.
> Whats it called?

The reason I ask: I sorely miss haskell's pattern matching in python.

It goes some way:

>>> ((x,y),z) = ((1,2),3)
>>> x,y,z
(1, 2, 3)

But not as far as I would like:

>>> ((x,y),3) = ((1,2),3)
  File "<stdin>", line 1
SyntaxError: can't assign to literal
>>> 

[Haskell]

Prelude> let (x, (y, (42, z, "Hello"))) = (1, (2, (42, 3, "Hello")))
Prelude> (x,y,z)
(1,2,3)