[PEP] matching and mismatching

[Jeff Epler]

On Thu, May 02, 2002 at 05:01:59PM +0000, Luke Kenneth Casson Leighton wrote:
> for x in ([1,3,2,5,9] matching lambda x:x > 2):
> 	print x

As another poster has observed, you can use list comprehensions for this
purpose, as long as constructing the temporary list is palatable.  Of
course,
    """ print non-empty lines """
    for x in file matching lambda x: len(strip(x)):
	print x
might avoid reading the entire file, but
    for x in [line in file if len(strip(line))]:
	print x
will force the construction of a list containing all the lines to be
printed.

There was a proposal to make 'generator comprehensions', with a syntax
like
    for x in [yield line in file if len(strip(line))]:
	print x
but it was rejected.  (http://python.org/peps/pep-0289.html)

Personally, if I got a vote, I would have been +1 on at least this part
of PEP 289, but it was rejected due to limited utility and difficulty of
implementation.

Jeff