What is a function parameter =[] for?

[Chris Angelico]

On Wed, Nov 25, 2015 at 11:36 AM, Steven D'Aprano <steve at pearwood.info> wrote:
> If, and only if, the tuple
> contains nothing but immutable constants e.g.
>
> (1, 2.0, None, "spam")
>
> then a sufficiently smart compiler may be able to treat that specific tuple
> as a constant/literal. But that's a special case, and cannot be generalised
> to all tuple displays.

In which case it's simply an example of constant-folding. It's the
same as (1+2j) being called up with LOAD_CONST, despite being an
expression. Recent CPythons are even willing to change what data type
something is, to make it a constant:

>>> dis.dis(lambda x: x in ["a","b","c","d","e"])
  1           0 LOAD_FAST                0 (x)
              3 LOAD_CONST               6 (('a', 'b', 'c', 'd', 'e'))
              6 COMPARE_OP               6 (in)
              9 RETURN_VALUE
>>> dis.dis(lambda x: x in {"a","b","c","d","e"})
  1           0 LOAD_FAST                0 (x)
              3 LOAD_CONST               6 (frozenset({'d', 'c', 'a',
'e', 'b'}))
              6 COMPARE_OP               6 (in)
              9 RETURN_VALUE

Lists and sets are definitely not constants. Tuples and frozensets
aren't literals, but they can be constant. This is the optimizer
talking, though, not language semantics.

ChrisA