dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Wednesday December 21 2011 18:00:23 Garth N. Wells wrote:
> What happens behind the scenes when for
> 
>    x = Vector(100)
> 
> ones does
> 
>   x[:]
> 
> ?

That depends if x[:] is on the lhs or on the rhs. If it is on the rhs a copy 
will be returned. This is a slice convention in Python.

  l0 = range(5)
  l1 = l[:]
  l1[0] = 1

The last statement will change l1 but not l0. I would expect the same for 
dolfin vectors.

If it is on lhs and the rhs is either a GeneriVector or a scalar, 
x._assign(rhs) will be envoked.

The relevant methods in la_post.i are:

  def __getslice__(...):
  def __setslize__(...):

Johan

 
> I've added GenericVector operator+= and -= for doubles, and would like
> to be sure that this can be used from Python without unnecessary
> copies being made.
> 
> Garth
> 
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