Martin v. Löwis wrote:
Mike Krell wrote:
Well, 3to2 would then be an option for you: use Python 3 as the source
language.
Making life easier for 3to2 is an *excellent* rationale for backports.
I'm skeptical. If new features get added to 2.7: why would that simplify
3to2? It couldn't *use* these features, since it surely would have to
support 2.6 and earlier as well.
Not sure what 3to2 would do about difficult-to-convert 3.x feature (as,
perhaps, the nonlocal keyword). If it currently gives up, it then may
offer you to restrict your target versions to 2.7+. Not sure whether
users would use that option, though - perhaps they rather stop using
nonlocal in 3.x if 3to2 cannot support it for all 2.x versions they are
interested in.
I would have thought you could translate nonlocal with the following:
Python 3:
def scope():
name = value
do_something_with(name)
def inner():
nonlocal name
name = new_value
do_something_else(name)
Python 2
def scope():
name = [value]
do_something_with(name[0])
def inner():
name[0] = new_value
do_something_else(name[0])
I would love to see nonlocal backported to 2.7 as it cleans up a simple
pattern that I use relatively often for testing.
Suppose you have an class and you want to test that method a calls
method b, in Python 2 you might write something like this:
def test_method_a_calls_method_b():
instance = SomeClass()
was_called = []
def method_b():
was_called.append(True)
instance.method_b = method_b
instance.method_a()
assert was_called == [True]
in Python 3 you can replace this with the slightly nicer:
def test_method_a_calls_method_b():
instance = SomeClass()
was_called = False
def method_b():
nonlocal was_called
was_called = True
instance.method_b = method_b
instance.method_a()
assert was_called
As to the argument that releasing 2.7 is pointless as few people would
use it for several years, the success of Python 2.6 shows that although
*many* people don't / can't use new versions of Python for several years
many other people are able to and do use new versions of Python.
All the best,
Michael Foord
Perhaps 3to2 has a work-around that still provides a good backport in
most cases. Then, the backport would not make the tool any simpler: if
3to2 would start using the backport, it would actually get more
complicated (not easier), as it now needs to support two cases.
Regards,
Martin
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
http://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
http://mail.python.org/mailman/options/python-dev/fuzzyman%40voidspace.org.uk
--
http://www.ironpythoninaction.com/
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
http://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
