Re: python3: accessing the result of 'if'

[Steve Holden]

Nick Coghlan wrote:

Carl Banks wrote:

What if the condition you wanted to test wasn't the same as the thing
you want to save?  In other words, how would you convert this?

. where:
.     m = something()
. if m > 20:
.     do_something_with(m)

Yeah, this problem eventually occurred to me as well. However, I think a little utility function can help solve it:

  def test(val, condition):
    if condition(val):
      return val
     else:
      return None

  if test(something(), lambda x: x < 10) as m:
    print "Case 1:", m
  elif test(something(), lambda x: x > 20) as m:
    print "Case 2:", m
  else:
    print "No case at all!"

If we were to use a where clause instead, it looks like:

  if test(something(), less_than(10)) as m:
    print "Case 1:", m
  elif test(something(), more_than(20)) as m:
    print "Case 2:", m
  else:
    print "No case at all!"
  where:
    def less_than(y):
      def lt(x):
        return x < y
      return lt

    def more_than(y):
      def gt(x):
        return x > y
      return lt

This is an example of why I don't think where clauses would completely eliminate the utility of deferred expressions. Here's a version using my preferred syntax from the AlternateLambdaSyntax page:

  if test(something(), (def x < 10 from x)) as m:
    print "Case 1:", m
  elif test(something(), (def x > 20 from x)) as m:
    print "Case 2:", m
  else:
    print "No case at all!"

Excuse me, these are supposed to be IMPROVEMENTS to Python?

regards
 Steve
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