[Python-Dev] list splicing (original) (raw)

Gareth McCaughan gmccaughan at synaptics-uk.com
Mon Sep 19 17:43:03 CEST 2005

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

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