[Python-ideas] PEP for executing a module in a package containing relative imports (original) (raw)

Jim Jewett jimjjewett at gmail.com
Sun Apr 22 00:03:03 CEST 2007

On 4/20/07, Brett Cannon <brett at python.org> wrote:

On 4/20/07, Steven Bethard <steven.bethard at gmail.com> wrote: > On 4/20/07, Brett Cannon <brett at python.org> wrote: > > On 4/19/07, Steven Bethard <steven.bethard at gmail.com> wrote:

> > > I would have thought that if Python inserted main before any of > > > the module contents got exec'd, it would be backwards compatible > > > because any use of main would just overwrite the default one.

> > That's right, and that is the problem. That would mean if main > > was false but then overwritten by a function or something, it suddenly > > became true. It isn't a problem in terms of whether the code will > > run, but whether the expected semantics will occur.

If the code is still using a main variable of its own, then presumably it isn't using the new meaning of main, and isn't affected by the unexpected semantics.

Or are you concerned that some code outside a module could check to see whether that module is main?

> Sure, but I don't see how it's much different from anyone who writes::

> list = [foo, bar, baz]

> and then later wonders why::

> list(obj)

> gives a TypeError: 'list' object is not callable.

Exactly. It's just that 'list' was known about when the code was written while main was not.

In that case, the module itself isn't using (and doesn't care) about the new main semantics. Code external to the module can't rely on either (list or main) being unchanged, even today.

> I'd really like there to be a way to write Python 3.0 compatible code > in Python 2.6 without having to run through 2to3.

To me, this is a fairly important requirement that I fear is sometimes being forgotten.

2to3 isn't really a one-time translation unless you stop supporting 2.x after running it.

-jJ

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