[Python-Dev] sort() return value

[Guido van Rossum]

I'd like to explain once more why I'm so adamant that sort() shouldn't
return 'self'.

This comes from a coding style (popular in various other languages, I
believe especially Lisp revels in it) where a series of side effects
on a single object can be chained like this:

  x.compress().chop(y).sort(z)

which would be the same as

  x.compress()
  x.chop(y)
  x.sort(z)

I find the chaining form a threat to readability; it requires that the
reader must be intimately familiar with each of the methods.  The
second form makes it clear that each of these calls acts on the same
object, and so even if you don't know the class and its methods very
well, you can understand that the second and third call are applied to
x (and that all calls are made for their side-effects), and not to
something else.

I'd like to reserve chaining for operations that return new values,
like string processing operations:

  y = x.rstrip("\n").split(":").lower()

There are a few standard library modules that encourage chaining of
side-effect calls (pstat comes to mind).  There shouldn't be any new
ones; pstat slipped through my filter when it was weak.

--Guido van Rossum (home page: http://www.python.org/~guido/)