The real problem with Python 3 - no business case for conversion (was "I strongly dislike Python 3")

[Martin v. Loewis]

> I just
> couldn't get through on the python-dev list that I couldn't just
> upgrade my code to 2.6 and then use 2to3 to keep in step across the
> 2-3 chasm, as this would leave behind my faithful pre-2.6 users.

Not sure whom you had been talking to. But I would have tried to explain
that you don't *have* to port to 2.6 to use 2to3 - it will
work just as fine with 2.3 code, and earlier.

> - No use of sets.  Instead I defined a very simple set simulation
> using dict keys, which could be interchanged with set for later
> versions.

This I don't understand. IIUC, you want to support 2.3 and later.
Now, 2.3 already has a set module, even though set is not a builtin.
So you could use sets just as well.

> - No generator expressions, only list comprehensions.

Ok. Not sure how this causes problems, though - just don't use them, then.

> - No use of decorators.  BUT, pyparsing includes a decorator method,
> traceParseAction, which can be used by users with later Pythons as
> @traceParseAction in their own code.

Of course, users of older Python versions could explicitly wrap
the functions with the decorator if they wanted to.

> - No print statements.  As pyparsing is intended to be an internal
> module, it does no I/O as part of its function - it only processes a
> given string, and returns a data structure.

If you don't need them, fine. If you do, I'd just let 2to3 transform them.

> - Python 2-3 compatible exception syntax.  This may have been my
> trickiest step.  The change of syntax for except from
> 
>     except ExceptionType, ex:
> 
> to:
> 
>     except ExceptionType as ex:
> 
> is completely forward and backward incompatible.  The workaround is to
> rewrite as:
> 
>     except ExceptionType:
>         ex = sys.exc_info()[0]

Likewise, and more importantly so: use 2to3. It can be done this way,
but I find the 2to3 solution much cleaner.

> But in
> the meantime, I am still able to support all versions of Python NOW,
> and I plan to continue doing so (albeit "support" for 2.x versions
> will eventually mean "continue to offer a frozen feature set, with
> minimal bug-fixing if any").

The same would have been possible if you had chosen to use 2to3.

Regards,
Martin