[Python-ideas] Introducing where clauses

Ben Finney ben+python at benfinney.id.au
Mon Jun 22 13:01:07 CEST 2009

Andrey Popp <8mayday at gmail.com> writes:

> Reading discussion on python-ideas about  "Accessing the result of
> comprehension's expression from the conditional", I've came to the
> idea of where clauses, similar to Haskell's.
> This solves the problem of recalculating of value multiple times. For
> example, in the following expression:
>     [(f(x), f(x)) for x in some_iterable if f(x) < 2]

New syntax isn't necessary to solve the above stated problem. For
example, the following existing syntax is also a solution::

    [(y, y) for y in (f(x) for x in some_iterable) if y < 2]

For the proposed new syntax to be accepted, it would need to be somehow
significantly superior to the existing syntax. Can you demonstrate how
it's superior?

 \        “I took a course in speed waiting. Now I can wait an hour in |
  `\                                 only ten minutes.” —Steven Wright |
_o__)                                                                  |
Ben Finney

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