[Python-Dev] list splicing

[Gareth McCaughan]

On Monday 2005-09-19 06:38, Josiah Carlson wrote:

> > >     [ 'x', *a, 'y']
> > >
> > > as syntactic sugar for
> > >
> > >     [ 'x' ] + a + [ 'y' ].
> > >
> > > Notes:
> > > - This is a common operation
> > 
> > is it?
> 
> Not in the code that I read/use.  While "not all 3 line functions should
> be a builtin", "not all <5 character typing savings should be made
> syntax".

The problems with syntax are

  1 It adds cognitive load.
  2 It makes your code look like line noise.
  3 It reduces options for future development.
  4 It complicates the parser.

In this instance, I don't think #1 applies; the rule "Putting *foo
into a comma-separated list is the same as putting all the elements
of foo into that list" isn't actually any harder to remember than
the current rule concerning the prefix-* operator.

#2 is always debatable. In this instance the proposed new form
doesn't look any uglier to me (I speak for no one else) than its
predecessor.

#3 surely isn't true here; there isn't anything else sensible
to do with prefix-* in lists, given the existing use specifically
in argument lists.

I don't know about #4, but I suspect it (along with the related
"it requires work, and there isn't much benefit from it") is the
best argument against this proposal.

-- 
g