Builtins.lazy for lazy arguments

[dg-pb]

@peterc

import some_lib

d = some_lib.their_dict({1:1, 2:2})
keys = [1,2,3]
for key in keys:
  a = d.get(key, lazy(lambda:3))
  if a == 3:
    ...
    #oops this never triggers

The problem I saw with the Backquotes for deferred expression,

I think I misunderstood last time what you meant. If you are referring to Backquotes for deferred expression, it actually has made it work quite nicely.

Even type(deferred_object) does the right thing by modifications in C. It works predictably and intuitively for Pure Python code, but a way to extend this to C extensions has not been found as far as I know, which is a major dealbreaker.