PEP new assert idiom

[Paul Rubin]

Some time ago I found myself proposing a new "Validate" statement,
which would work exactly like "assert", except:

  1) it would throw a ValidationError instead of AssertionError
     if the condition failed

  2) it would NOT be turned into a no-op by the optimizing compiler.

The purpose is runtime validation of user data, rather than sanity
checking the program logic.  Example: I keep finding myself writing
code like:

    x = float(raw_input('Enter a positive number: '))
    assert x > 0, 'number wasn't positive'

This is incorrect because the assert statement is not guaranteed to be
executed.  I propose to say instead,

   validate x > 0, 'number wasn't positive'

which would do the right thing.

This proposal was reasonably well received when I've posted it before,
but I don't remember if there was any conclusion, and there was no
follow-up.  Since we're again talking about PEP's regarding the assert
statement, should I try to put one together for this, in my copious
(hah) free time?